title: rxjs flatmap missing
body: <p>I try to chain multiple rx.js observables and pass the data. <code>Flatmap</code> should be the fitting operator but with an import of</p>
  
  <pre><code>import { Observable } from 'rxjs/Observable';
  </code></pre>
  
  <p>it is not found:</p>
  
  <pre><code>Error TS2339: Property 'flatmap' does not exist on type 'Observable&lt;Coordinates&gt;'
  </code></pre>
  
  <p>Version <code>5.0.0-beta.6</code> of rx.js is used.</p>
  
  <pre><code>public getCurrentLocationAddress():Observable&lt;String&gt; {
      return Observable.fromPromise(Geolocation.getCurrentPosition())
        .map(location =&gt; location.coords)
        .flatmap(coordinates =&gt; {
          console.log(coordinates);
          return this.http.request(this.geoCodingServer + "/json?latlng=" + coordinates.latitude + "," + coordinates.longitude)
            .map((res: Response) =&gt; {
                         let data = res.json();
                         return data.results[0].formatted_address;
                });
        });
    }
  </code></pre>