add missing permitted param

app/controllers/admin/hooks_controller.rb

@@ -62,6 +62,7 @@ class Admin::HooksController < Admin::ApplicationController
       :push_events,
       :tag_push_events,
       :repository_update_events,
+      :merge_requests_events,
       :token,
       :url
     )

spec/controllers/admin/hooks_controller_spec.rb

@@ -14,6 +14,7 @@ describe Admin::HooksController do
         push_events: true,
         tag_push_events: true,
         repository_update_events: true,
+        merge_requests_events: true,
         token: "TEST TOKEN",
         url: "http://example.com"
       }