Use gitlab-shell 1.7.8

lib/tasks/gitlab/check.rake

@@ -736,7 +736,7 @@ namespace :gitlab do
   end
   def check_gitlab_shell
-    required_version = Gitlab::VersionInfo.new(1, 7, 4)
+    required_version = Gitlab::VersionInfo.new(1, 7, 8)
     current_version = Gitlab::VersionInfo.parse(gitlab_shell_version)
     print "GitLab Shell version >= #{required_version} ? ... "