title: Angular2 rxjs missing observable.interval method
body: <p>I'm trying to use the interval method of an observable but I keep getting the error </p>
  
  <pre><code> Property 'interval' does not exist on type 'Observable&lt;any&gt;'.
  </code></pre>
  
  <p>I added these imports:</p>
  
  <pre><code>import "rxjs/Rx";
  import "rxjs/add/observable/interval";
  import "rxjs/observable/IntervalObservable";
  </code></pre>