Fix procfile and attachment in event nore

Procfile

 web: bundle exec unicorn_rails -p $PORT
-worker: bundle exec sidekiq -q post_receive,mailer,system_hook,project_web_hook,common,default,gitolite
+worker: bundle exec sidekiq -q post_receive,mailer,system_hook,project_web_hook,common,default,gitlab_shell

app/views/events/event/_note.html.haml

@@ -25,6 +25,7 @@
   %span.event-note
     = markdown truncate(event.target.note, length: 70)
     - note = event.target
+    - if note.attachment.url
       = link_to note.attachment.url, target: "_blank", class: 'note-file-attach' do
         - if note.attachment.image?
           = image_tag note.attachment.url, class: 'note-image-attach'