Add arm64 arch to release task; Bump Golang version to 1.10.2

Dockerfile.build.alpine

@@ -1,4 +1,4 @@
-FROM golang:1.9.1-alpine
+FROM golang:1.10.2-alpine
 
 RUN apk add --no-cache make git
 RUN mkdir -p /go/src/github.com/kelseyhightower/confd && \

Makefile

@@ -36,3 +36,5 @@ release:
 		if [ $$platform == windows ]; then extension=.exe; fi; \
 		docker run -it --rm -v ${PWD}:/app -e "GOOS=$$platform" -e "GOARCH=amd64" -e "CGO_ENABLED=0" confd_builder go build -ldflags="-s -w -X main.GitSHA=${GIT_SHA}" -o bin/confd-${VERSION}-$$platform-amd64$$extension; \
 	done
+	@docker run -it --rm -v ${PWD}:/app -e "GOOS=linux" -e "GOARCH=arm64" -e "CGO_ENABLED=0" confd_builder go build -ldflags="-s -w -X main.GitSHA=${GIT_SHA}" -o bin/confd-${VERSION}-linux-arm64;
+	@upx bin/confd-${VERSION}-*

README.md

@@ -17,7 +17,7 @@
 
 ## Building
 
-Go 1.8 is required to build confd, which uses the new vendor directory.
+Go 1.10 is required to build confd, which uses the new vendor directory.
 
 ```
 $ mkdir -p $GOPATH/src/github.com/kelseyhightower