Update to Go 1.13 (#38)

rox/Dockerfile

@@ -89,12 +89,12 @@ RUN set -ex \
 
 # Install Go
 # https://golang.org/dl/
-ARG GOLANG_VERSION=1.12.9
-ARG GOLANG_SHA256=ac2a6efcc1f5ec8bdc0db0a988bb1d301d64b6d61b7e8d9e42f662fbb75a2b9b
+ARG GOLANG_VERSION=1.13
+ARG GOLANG_SHA256=68a2297eb099d1a76097905a2ce334e3155004ec08cdea85f24527be3c48e856
 ENV GOPATH=/go
 ENV PATH=$GOPATH/bin:/usr/local/go/bin:$PATH
 RUN set -ex \
- && url="https://golang.org/dl/go${GOLANG_VERSION}.linux-amd64.tar.gz" \
+ && url="https://dl.google.com/go/go${GOLANG_VERSION}.linux-amd64.tar.gz" \
  && wget --no-verbose -O go.tgz "$url" \
  && echo "${GOLANG_SHA256} *go.tgz" | sha256sum -c - \
  && tar -C /usr/local -xzf go.tgz \
@@ -104,24 +104,6 @@ RUN set -ex \
  && chmod -R 777 "$GOPATH" \
  && chown -R circleci "$GOPATH"
 
-# Add necessary Go build tools
-RUN set -ex \
- && go get -u golang.org/x/lint/golint \
- && command -v golint \
- && go get -d golang.org/x/tools/cmd/goimports \
- && cd "$GOPATH/src/golang.org/x/tools" \
- && git checkout -q 0268d3dd0724eb8b65d4e71a1285076f6efd643d \
- && go install golang.org/x/tools/cmd/goimports \
- && command -v goimports \
- && go get -u github.com/jstemmer/go-junit-report \
- && command -v go-junit-report \
- && wget --no-verbose -O $GOPATH/bin/dep https://github.com/golang/dep/releases/download/v0.5.0/dep-linux-amd64 \
- && chmod +x $GOPATH/bin/dep \
- && command -v dep \
- && go get github.com/mattn/goveralls \
- && command -v goveralls \
- && rm -rf $GOPATH/src/* $GOPATH/pkg/*
-
 # Install gcloud
 # gcloud prefers to run out of a user's home directory.
 ARG GCLOUD_VERSION=253.0.0