diff --git a/vendor.conf b/vendor.conf
index 0213e2b93a..9f28c181dc 100644
--- a/vendor.conf
+++ b/vendor.conf
@@ -150,7 +150,7 @@ github.com/prometheus/client_model                  6f3806018612930941127f2a7c6c
 github.com/prometheus/common                        7600349dcfe1abd18d72d3a1770870d9800a7801
 github.com/prometheus/procfs                        7d6f385de8bea29190f15ba9931442a0eaef9af7
 github.com/matttproud/golang_protobuf_extensions    c12348ce28de40eed0136aa2b644d0ee0650e56c # v1.0.1
-github.com/pkg/errors                               645ef00459ed84a119197bfb8d8205042c6df63d # v0.8.0
+github.com/pkg/errors                               ba968bfe8b2f7e042a574c888954fccecfa385b4 # v0.8.1
 github.com/grpc-ecosystem/go-grpc-prometheus        c225b8c3b01faf2899099b768856a9e916e5087b # v1.2.0
 
 # cli
diff --git a/vendor/github.com/pkg/errors/README.md b/vendor/github.com/pkg/errors/README.md
index 273db3c98a..6483ba2afb 100644
--- a/vendor/github.com/pkg/errors/README.md
+++ b/vendor/github.com/pkg/errors/README.md
@@ -1,4 +1,4 @@
-# errors [![Travis-CI](https://travis-ci.org/pkg/errors.svg)](https://travis-ci.org/pkg/errors) [![AppVeyor](https://ci.appveyor.com/api/projects/status/b98mptawhudj53ep/branch/master?svg=true)](https://ci.appveyor.com/project/davecheney/errors/branch/master) [![GoDoc](https://godoc.org/github.com/pkg/errors?status.svg)](http://godoc.org/github.com/pkg/errors) [![Report card](https://goreportcard.com/badge/github.com/pkg/errors)](https://goreportcard.com/report/github.com/pkg/errors)
+# errors [![Travis-CI](https://travis-ci.org/pkg/errors.svg)](https://travis-ci.org/pkg/errors) [![AppVeyor](https://ci.appveyor.com/api/projects/status/b98mptawhudj53ep/branch/master?svg=true)](https://ci.appveyor.com/project/davecheney/errors/branch/master) [![GoDoc](https://godoc.org/github.com/pkg/errors?status.svg)](http://godoc.org/github.com/pkg/errors) [![Report card](https://goreportcard.com/badge/github.com/pkg/errors)](https://goreportcard.com/report/github.com/pkg/errors) [![Sourcegraph](https://sourcegraph.com/github.com/pkg/errors/-/badge.svg)](https://sourcegraph.com/github.com/pkg/errors?badge)
 
 Package errors provides simple error handling primitives.
 
@@ -47,6 +47,6 @@ We welcome pull requests, bug fixes and issue reports. With that said, the bar f
 
 Before proposing a change, please discuss your change by raising an issue.
 
-## Licence
+## License
 
 BSD-2-Clause
diff --git a/vendor/github.com/pkg/errors/errors.go b/vendor/github.com/pkg/errors/errors.go
index 842ee80456..7421f326ff 100644
--- a/vendor/github.com/pkg/errors/errors.go
+++ b/vendor/github.com/pkg/errors/errors.go
@@ -6,7 +6,7 @@
 //             return err
 //     }
 //
-// which applied recursively up the call stack results in error reports
+// which when applied recursively up the call stack results in error reports
 // without context or debugging information. The errors package allows
 // programmers to add context to the failure path in their code in a way
 // that does not destroy the original value of the error.
@@ -15,16 +15,17 @@
 //
 // The errors.Wrap function returns a new error that adds context to the
 // original error by recording a stack trace at the point Wrap is called,
-// and the supplied message. For example
+// together with the supplied message. For example
 //
 //     _, err := ioutil.ReadAll(r)
 //     if err != nil {
 //             return errors.Wrap(err, "read failed")
 //     }
 //
-// If additional control is required the errors.WithStack and errors.WithMessage
-// functions destructure errors.Wrap into its component operations of annotating
-// an error with a stack trace and an a message, respectively.
+// If additional control is required, the errors.WithStack and
+// errors.WithMessage functions destructure errors.Wrap into its component
+// operations: annotating an error with a stack trace and with a message,
+// respectively.
 //
 // Retrieving the cause of an error
 //
@@ -38,7 +39,7 @@
 //     }
 //
 // can be inspected by errors.Cause. errors.Cause will recursively retrieve
-// the topmost error which does not implement causer, which is assumed to be
+// the topmost error that does not implement causer, which is assumed to be
 // the original cause. For example:
 //
 //     switch err := errors.Cause(err).(type) {
@@ -48,16 +49,16 @@
 //             // unknown error
 //     }
 //
-// causer interface is not exported by this package, but is considered a part
-// of stable public API.
+// Although the causer interface is not exported by this package, it is
+// considered a part of its stable public interface.
 //
 // Formatted printing of errors
 //
 // All error values returned from this package implement fmt.Formatter and can
-// be formatted by the fmt package. The following verbs are supported
+// be formatted by the fmt package. The following verbs are supported:
 //
 //     %s    print the error. If the error has a Cause it will be
-//           printed recursively
+//           printed recursively.
 //     %v    see %s
 //     %+v   extended format. Each Frame of the error's StackTrace will
 //           be printed in detail.
@@ -65,13 +66,13 @@
 // Retrieving the stack trace of an error or wrapper
 //
 // New, Errorf, Wrap, and Wrapf record a stack trace at the point they are
-// invoked. This information can be retrieved with the following interface.
+// invoked. This information can be retrieved with the following interface:
 //
 //     type stackTracer interface {
 //             StackTrace() errors.StackTrace
 //     }
 //
-// Where errors.StackTrace is defined as
+// The returned errors.StackTrace type is defined as
 //
 //     type StackTrace []Frame
 //
@@ -85,8 +86,8 @@
 //             }
 //     }
 //
-// stackTracer interface is not exported by this package, but is considered a part
-// of stable public API.
+// Although the stackTracer interface is not exported by this package, it is
+// considered a part of its stable public interface.
 //
 // See the documentation for Frame.Format for more details.
 package errors
@@ -192,7 +193,7 @@ func Wrap(err error, message string) error {
 }
 
 // Wrapf returns an error annotating err with a stack trace
-// at the point Wrapf is call, and the format specifier.
+// at the point Wrapf is called, and the format specifier.
 // If err is nil, Wrapf returns nil.
 func Wrapf(err error, format string, args ...interface{}) error {
 	if err == nil {
@@ -220,6 +221,18 @@ func WithMessage(err error, message string) error {
 	}
 }
 
+// WithMessagef annotates err with the format specifier.
+// If err is nil, WithMessagef returns nil.
+func WithMessagef(err error, format string, args ...interface{}) error {
+	if err == nil {
+		return nil
+	}
+	return &withMessage{
+		cause: err,
+		msg:   fmt.Sprintf(format, args...),
+	}
+}
+
 type withMessage struct {
 	cause error
 	msg   string
diff --git a/vendor/github.com/pkg/errors/stack.go b/vendor/github.com/pkg/errors/stack.go
index 6b1f2891a5..2874a048cf 100644
--- a/vendor/github.com/pkg/errors/stack.go
+++ b/vendor/github.com/pkg/errors/stack.go
@@ -46,7 +46,8 @@ func (f Frame) line() int {
 //
 // Format accepts flags that alter the printing of some verbs, as follows:
 //
-//    %+s   path of source file relative to the compile time GOPATH
+//    %+s   function name and path of source file relative to the compile time
+//          GOPATH separated by \n\t (<funcname>\n\t<path>)
 //    %+v   equivalent to %+s:%d
 func (f Frame) Format(s fmt.State, verb rune) {
 	switch verb {
@@ -79,6 +80,14 @@ func (f Frame) Format(s fmt.State, verb rune) {
 // StackTrace is stack of Frames from innermost (newest) to outermost (oldest).
 type StackTrace []Frame
 
+// Format formats the stack of Frames according to the fmt.Formatter interface.
+//
+//    %s	lists source files for each Frame in the stack
+//    %v	lists the source file and line number for each Frame in the stack
+//
+// Format accepts flags that alter the printing of some verbs, as follows:
+//
+//    %+v   Prints filename, function, and line number for each Frame in the stack.
 func (st StackTrace) Format(s fmt.State, verb rune) {
 	switch verb {
 	case 'v':
@@ -136,43 +145,3 @@ func funcname(name string) string {
 	i = strings.Index(name, ".")
 	return name[i+1:]
 }
-
-func trimGOPATH(name, file string) string {
-	// Here we want to get the source file path relative to the compile time
-	// GOPATH. As of Go 1.6.x there is no direct way to know the compiled
-	// GOPATH at runtime, but we can infer the number of path segments in the
-	// GOPATH. We note that fn.Name() returns the function name qualified by
-	// the import path, which does not include the GOPATH. Thus we can trim
-	// segments from the beginning of the file path until the number of path
-	// separators remaining is one more than the number of path separators in
-	// the function name. For example, given:
-	//
-	//    GOPATH     /home/user
-	//    file       /home/user/src/pkg/sub/file.go
-	//    fn.Name()  pkg/sub.Type.Method
-	//
-	// We want to produce:
-	//
-	//    pkg/sub/file.go
-	//
-	// From this we can easily see that fn.Name() has one less path separator
-	// than our desired output. We count separators from the end of the file
-	// path until it finds two more than in the function name and then move
-	// one character forward to preserve the initial path segment without a
-	// leading separator.
-	const sep = "/"
-	goal := strings.Count(name, sep) + 2
-	i := len(file)
-	for n := 0; n < goal; n++ {
-		i = strings.LastIndex(file[:i], sep)
-		if i == -1 {
-			// not enough separators found, set i so that the slice expression
-			// below leaves file unmodified
-			i = -len(sep)
-			break
-		}
-	}
-	// get back to 0 or trim the leading separator
-	file = file[i+len(sep):]
-	return file
-}