Merge branch 'warning' into 'master'

remove make warning

When building gitlab-workhose a warning is printed out. This merge request fixes the warning

```
go build -ldflags "-X main.Version 0.5.1-20160103.233349" -o gitlab-workhorse
# _/home/git/gitlab-workhorse
link: warning: option -X main.Version 0.5.1-20160103.233349 may not work in future releases; use -X main.Version=0.5.1-20160103.233349
```

See merge request !22

Makefile

@@ -2,7 +2,7 @@ PREFIX=/usr/local
 VERSION=$(shell git describe)-$(shell date -u +%Y%m%d.%H%M%S)
 
 gitlab-workhorse: $(wildcard *.go)
-	go build -ldflags "-X main.Version ${VERSION}" -o gitlab-workhorse
+	go build -ldflags "-X main.Version=${VERSION}" -o gitlab-workhorse
 
 install: gitlab-workhorse
 	install gitlab-workhorse ${PREFIX}/bin/