chore: update go toolchain to 1.12.2 (#959)

See https://github.com/deis/docker-go-dev/releases/tag/v1.21.0
and https://github.com/golang/go/issues?q=milestone%3AGo1.12.2

.pipelines/pr-e2e.yaml

@@ -17,7 +17,7 @@ pr:
 resources:
   containers:
   - container: dev1
-    image: quay.io/deis/go-dev:v1.19.2
+    image: quay.io/deis/go-dev:v1.21.0
 
 jobs:
 - job: unit_tests

Makefile

@@ -25,7 +25,7 @@ GITTAG := $(VERSION_SHORT)
 endif
 
 REPO_PATH := github.com/Azure/$(PROJECT)
-DEV_ENV_IMAGE := quay.io/deis/go-dev:v1.19.2
+DEV_ENV_IMAGE := quay.io/deis/go-dev:v1.21.0
 DEV_ENV_WORK_DIR := /go/src/${REPO_PATH}
 DEV_ENV_OPTS := --rm -v ${CURDIR}:${DEV_ENV_WORK_DIR} -w ${DEV_ENV_WORK_DIR} ${DEV_ENV_VARS}
 DEV_ENV_CMD := docker run ${DEV_ENV_OPTS} ${DEV_ENV_IMAGE}

makedev.ps1

@@ -1,5 +1,5 @@
 $REPO_PATH = "github.com/Azure/aks-engine"
-$DEV_ENV_IMAGE = "quay.io/deis/go-dev:v1.19.2"
+$DEV_ENV_IMAGE = "quay.io/deis/go-dev:v1.21.0"
 $DEV_ENV_WORK_DIR = "/go/src/$REPO_PATH"
 
 docker.exe run -it --rm -w $DEV_ENV_WORK_DIR -v `"$($PWD)`":$DEV_ENV_WORK_DIR $DEV_ENV_IMAGE bash