fix quick submit missing in edit merge request page

app/views/projects/merge_requests/_form.html.haml

-= form_for [@project.namespace.becomes(Namespace), @project, @merge_request], html: { class: 'merge-request-form form-horizontal gfm-form js-requires-input' } do |f|
+= form_for [@project.namespace.becomes(Namespace), @project, @merge_request], html: { class: 'merge-request-form form-horizontal gfm-form js-requires-input js-quick-submit' } do |f|
   = render 'shared/issuable/form', f: f, issuable: @merge_request
 
 :javascript