docs(structural-directives): change "JavaScript cycle" to "browser event loop"

closes #710

It makes more sense since where gonna use it in Typescript and Dart as well.

public/docs/_examples/structural-directives/ts/app/heavy-loader.component.ts

@@ -28,7 +28,7 @@ export class HeavyLoaderComponent {
   }
 
   // Triggers the next round of Angular change detection
-  // after one turn of the JavaScript cycle
+  // after one turn of the browser event loop
   // ensuring display of msg added in onDestroy
   private _tick() { setTimeout(() => { }, 0); }
 }