Use gitlab-workhorse 0.7.4

This enables
https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/4278 .

GITLAB_WORKHORSE_VERSION

-0.7.3
+0.7.4

doc/install/installation.md

@@ -394,7 +394,7 @@ GitLab Shell is an SSH access and repository management software developed speci
     cd /home/git
     sudo -u git -H git clone https://gitlab.com/gitlab-org/gitlab-workhorse.git
     cd gitlab-workhorse
-    sudo -u git -H git checkout v0.7.3
+    sudo -u git -H git checkout v0.7.4
     sudo -u git -H make
 
 ### Initialize Database and Activate Advanced Features