Require gitlab-shell v1.8.4

Signed-off-by: Dmitriy Zaporozhets <dmitriy.zaporozhets@gmail.com>

lib/tasks/gitlab/check.rake

@@ -727,7 +727,7 @@ namespace :gitlab do
   end
 
   def check_gitlab_shell
-    required_version = Gitlab::VersionInfo.new(1, 7, 9)
+    required_version = Gitlab::VersionInfo.new(1, 8, 4)
     current_version = Gitlab::VersionInfo.parse(gitlab_shell_version)
 
     print "GitLab Shell version >= #{required_version} ? ... "