Calculate build coverage asynchronously

app/models/ci/build.rb

@@ -82,9 +82,8 @@ module Ci
       end
 
       after_transition any => [:success, :failed, :canceled] do |build|
-        build.update_coverage
-
         build.run_after_commit do
+          BuildCoverageWorker.perform_async(id)
           BuildHooksWorker.perform_async(id)
         end
       end