Adapte "make update" to gitlab-workhorse GOPATH

Makefile

 gitlab_repo = https://gitlab.com/gitlab-org/gitlab-ce.git
 gitlab_shell_repo = https://gitlab.com/gitlab-org/gitlab-shell.git
 gitlab_workhorse_repo = https://gitlab.com/gitlab-org/gitlab-workhorse.git
+gitlab_workhorse_clone_dir = gitlab-workhorse/src/gitlab.com/gitlab-org/gitlab-workhorse
 gitlab_development_root = $(shell pwd)
 postgres_bin_dir = $(shell pg_config --bindir)
 postgres_replication_user = gitlab_replication
@@ -151,17 +152,19 @@ localhost.key:
 gitlab-workhorse-setup: gitlab-workhorse/bin/gitlab-workhorse
-gitlab-workhorse-update: gitlab-workhorse/.git/pull
-	make
-gitlab-workhorse/bin/gitlab-workhorse: gitlab-workhorse/src/gitlab.com/gitlab-org/gitlab-workhorse/.git
+gitlab-workhorse-update: gitlab-workhorse/.git/pull gitlab-workhorse-clean-bin gitlab-workhorse/bin/gitlab-workhorse
+gitlab-workhorse-clean-bin:
+	rm -rf gitlab-workhorse/bin
+
+gitlab-workhorse/bin/gitlab-workhorse: ${gitlab_workhorse_clone_dir}/.git
 	GOPATH=${gitlab_development_root}/gitlab-workhorse go install gitlab.com/gitlab-org/gitlab-workhorse/...
-gitlab-workhorse/src/gitlab.com/gitlab-org/gitlab-workhorse/.git:
-	git clone ${gitlab_workhorse_repo} gitlab-workhorse/src/gitlab.com/gitlab-org/gitlab-workhorse
+${gitlab_workhorse_clone_dir}/.git:
+	git clone ${gitlab_workhorse_repo} ${gitlab_workhorse_clone_dir}
 gitlab-workhorse/.git/pull:
-	cd ${gitlab_development_root}/gitlab-workhorse && \
+	cd ${gitlab_workhorse_clone_dir} && \
 		git stash &&\
 		git checkout master &&\
 		git pull --ff-only