Use gitlab-workhorse 0.8.1

This adds (basic) Sentry support.

GITLAB_WORKHORSE_VERSION

-0.8.0
+0.8.1

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 v0.8.0
+    sudo -u git -H git checkout v0.8.1
     sudo -u git -H make
 
 ### Initialize Database and Activate Advanced Features

doc/update/8.11-to-8.12.md

@@ -82,7 +82,7 @@ GitLab 8.1.
 ```bash
 cd /home/git/gitlab-workhorse
 sudo -u git -H git fetch --all
-sudo -u git -H git checkout v0.8.0
+sudo -u git -H git checkout v0.8.1
 sudo -u git -H make
 ```