Use run_after_commit to avoid race condition, feedback:

https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/6342/diffs#note_17038749

app/models/ci/pipeline.rb

@@ -84,9 +84,11 @@ module Ci
       end
       after_transition any => [:success, :failed] do |pipeline|
+        pipeline.run_after_commit do
           SendPipelineNotificationWorker.perform_async(pipeline.id)
         end
       end
+    end
     # ref can't be HEAD or SHA, can only be branch/tag name
     def self.latest_successful_for(ref)