Add new make rule for smaller go binaries (#660)

Running upx on go binaries reduces binary size ~ from 7MB -> 1.5MB

README.md

@@ -86,3 +86,8 @@ make test-heroku-16
 The tests are run via the vendored
 [shunit2](https://github.com/kward/shunit2)
 test framework.
+
+## Updating go binaries
+
+If you would like to develop and update the go binaries you will need to install 
+[go 1.12](https://golang.org/doc/install#install) and [upx](https://upx.github.io/)

makefile

@@ -4,6 +4,14 @@ build:
 	@GOOS=darwin GOARCH=amd64 go build -ldflags="-s -w" -v -o ./vendor/resolve-version-darwin ./cmd/resolve-version
 	@GOOS=linux GOARCH=amd64 go build -ldflags="-s -w" -v -o ./vendor/resolve-version-linux ./cmd/resolve-version
 
+build-production:
+	# build go binaries and then compress them
+	@GOOS=darwin GOARCH=amd64 go build -ldflags="-s -w" -v -o ./vendor/resolve-version-darwin ./cmd/resolve-version
+	@GOOS=linux GOARCH=amd64 go build -ldflags="-s -w" -v -o ./vendor/resolve-version-linux ./cmd/resolve-version
+	# https://blog.filippo.io/shrink-your-go-binaries-with-this-one-weird-trick/
+	upx --brute vendor/resolve-version-linux
+	upx --brute vendor/resolve-version-darwin
+
 test-binary:
 	go test -v ./cmd/... -tags=integration