Merge branch 'gitlab-workhorse-0.8.4' into 'master'

Use gitlab-workhorse 0.8.4

Fixes Go 1.5 compatibility broken in 0.8.3.

See merge request !6712

GITLAB_WORKHORSE_VERSION

-0.8.2
+0.8.4

doc/install/installation.md

@@ -400,7 +400,7 @@ If you are not using Linux you may have to run `gmake` instead of
     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 v0.8.2
+    sudo -u git -H git checkout v0.8.4
     sudo -u git -H make
 
 ### Initialize Database and Activate Advanced Features

doc/update/8.12-to-8.13.md

@@ -84,7 +84,7 @@ GitLab 8.1.
 ```bash
 cd /home/git/gitlab-workhorse
 sudo -u git -H git fetch --all
-sudo -u git -H git checkout v0.8.2
+sudo -u git -H git checkout v0.8.4
 sudo -u git -H make
 ```