Update toolchain to Go 1.12.8 (#6319)

Author: mkeeler

.circleci/config.yml

@@ -3,7 +3,7 @@ version: 2
 
 references:
   images:
-    go: &GOLANG_IMAGE circleci/golang:1.12.1
+    go: &GOLANG_IMAGE circleci/golang:1.12.8
     middleman: &MIDDLEMAN_IMAGE hashicorp/middleman-hashicorp:0.3.35
     ember: &EMBER_IMAGE circleci/node:8-browsers
 

build-support/docker/Build-Go.dockerfile

@@ -1,4 +1,4 @@
-ARG GOLANG_VERSION=1.12.1
+ARG GOLANG_VERSION=1.12.8
 FROM golang:${GOLANG_VERSION}
 
 ARG GOTOOLS="github.com/elazarl/go-bindata-assetfs/... \

build-support/docker/Test-Flake.dockerfile

@@ -1,6 +1,6 @@
 FROM travisci/ci-garnet:packer-1512502276-986baf0
 
-ENV GOLANG_VERSION 1.10.3
+ENV GOLANG_VERSION 1.12.8
 
 RUN mkdir -p /home/travis/go && chown -R travis /home/travis/go