gitlab: Sync launch of gitlab-workhorse service with upstream

add `-documentRoot ...` argument to gitlab-workhorse start as upstream
started to do:

    https://gitlab.com/gitlab-org/omnibus-gitlab/commit/d769f751

( gitlab-workhorse now needs to know where document root is as it now
  serves all content - e.g. static files too

  this option was introduced here:

    https://gitlab.com/gitlab-org/gitlab-workhorse/commit/1a7009e4  )

/cc @kazuhiko, @jerome

software/gitlab/instance-gitlab.cfg.in

@@ -514,6 +514,7 @@ command-line    = {{ gitlab_workhorse }}
     -listenNetwork unix
     -listenAddr ${gitlab-workhorse:socket}
     -authSocket ${unicorn:socket}
+    -documentRoot ${gitlab-work:location}/public
 # NOTE for profiling
 #   -pprofListenAddr ...
 

software/gitlab/software.cfg

@@ -247,7 +247,7 @@ md5sum  = 97b7f5654bc280542ee348cb6fa60893
 
 [instance-gitlab.cfg.in]
 <= download-file
-md5sum  = 293b45fc69562c057819e3a876acaa54
+md5sum  = 0d4b88fdadd315189199b160435bd82e
 
 [macrolib.cfg.in]
 <= download-file