Bump Golang 1.12.6

Signed-off-by: Jintao Zhang <zhangjintao9020@gmail.com>

Dockerfile

@@ -26,7 +26,7 @@
 
 ARG CROSS="false"
 
-FROM golang:1.12.5 AS base
+FROM golang:1.12.6 AS base
 # allow replacing httpredir or deb mirror
 ARG APT_MIRROR=deb.debian.org
 RUN sed -ri "s/(httpredir|deb).debian.org/$APT_MIRROR/g" /etc/apt/sources.list

Dockerfile.e2e

@@ -1,4 +1,4 @@
-FROM golang:1.12.5-alpine as base
+FROM golang:1.12.6-alpine as base
 
 RUN apk --no-cache add \
     bash \

Dockerfile.simple

@@ -5,7 +5,7 @@
 
 # This represents the bare minimum required to build and test Docker.
 
-FROM golang:1.12.5
+FROM golang:1.12.6
 
 # allow replacing httpredir or deb mirror
 ARG APT_MIRROR=deb.debian.org

Dockerfile.windows

@@ -168,7 +168,7 @@ SHELL ["powershell", "-Command", "$ErrorActionPreference = 'Stop'; $ProgressPref
 # Environment variable notes:
 #  - GO_VERSION must be consistent with 'Dockerfile' used by Linux.
 #  - FROM_DOCKERFILE is used for detection of building within a container.
-ENV GO_VERSION=1.12.5 `
+ENV GO_VERSION=1.12.6 `
     GIT_VERSION=2.11.1 `
     GOPATH=C:\go `
     FROM_DOCKERFILE=1