Run lastBuildDidChange only once for a runloop run

When a lot of pusher events come with build updates, lastBuildDidChange
can run quite frequently. We can avoid that by using scheduleOnce, which
will ensure that only the last invocation of lastBuildDidChange will be
run for a given runloop run.

assets/scripts/app/controllers/repo.coffee

@@ -50,6 +50,9 @@ Travis.RepoController = Travis.Controller.extend
     @connectTab('job')
 
   lastBuildDidChange: ->
+    Ember.run.scheduleOnce('data', this, @_lastBuildDidChange);
+
+  _lastBuildDidChange: ->
     build = @get('repo.lastBuild')
     @set('build', build)