title: angular 2.0 ngClass is not updated on timeout
body: <p>I'm using Angular 2.0 beta 15.</p>
  
  <p>Initially I was experiencing this problem while developing an app. Then I decided to try the simplest possible case to reproduce it. See the code below</p>
  
  <pre><code>//our root app component
  import {Component} from 'angular2/core'
  
  @Component({
    selector: 'my-app',
    providers: [],
    template: `
      &lt;div&gt;
        &lt;h2 [ngClass]="{'red-heading':isAlertOn, 'blue-heading':!isAlertOn}"&gt;Hello {{name}}&lt;/h2&gt;
      &lt;/div&gt;
    `,
    directives: []
  })
  export class App {
    isAlertOn:boolean;
  
    constructor() {
      this.name = 'Angular2';
      this.isAlertOn = false;
    }
  
    (function(){
      setTimeout(function(){
        console.log("in here");
        this.isAlertOn = true;
      },2000);
    })();
  }
  </code></pre>
  
  <p><a href="http://plnkr.co/edit/oro6VHGiFMm3wesCfzyb?p=preview" rel="nofollow">Plnkr</a></p>
  
  <p>Since I'm using animations in my application I want to trigget class changing with a delay. In order to do that I'm using setTimeout.</p>
  
  <p>I've read that in general all the changes are handled by NgZone manually (for some older alpha version I think). Right now those changes should be handled automatically. Either I'm missing something (still new in angular 2.0) or there might be a different approach.</p>
  
  <p>Thank you in advance guys.</p>