Bump vendor kr/pty to commit 3b1f6487b (syscall.O_NOCTTY)

hack/vendor.sh

@@ -21,7 +21,7 @@ git_clone () {
   )
 }
 
-git_clone github.com/kr/pty 27435c699
+git_clone github.com/kr/pty 3b1f6487b
 
 git_clone github.com/gorilla/context/ 708054d61e5
 

vendor/src/github.com/kr/pty/pty_linux.go

@@ -28,7 +28,7 @@ func open() (pty, tty *os.File, err error) {
 		return nil, nil, err
 	}
 
-	t, err := os.OpenFile(sname, os.O_RDWR, 0)
+	t, err := os.OpenFile(sname, os.O_RDWR|syscall.O_NOCTTY, 0)
 	if err != nil {
 		return nil, nil, err
 	}