Pass GL_ID to the gitlab-shell update hook

With gitlab-shell 1.9.0 we always need to pass GL_ID because the update
hook no longer makes an exception for HTTP pushes.

Author: jacobvosmaer

Diff for: lib/grack/server.rb

@@ -272,7 +272,7 @@ def popen_options
     end
 
     def popen_env
-      {'PATH' => ENV['PATH']}
+      {'PATH' => ENV['PATH'], 'GL_ID' => ENV['GL_ID']}
     end
 
     # --------------------------------------