title: Subscribe to an AngularFireObject
body: <p>I just upgraded to AngularFire2 rc 5.0.</p>
  
  <p>I adapted my code so that it matches the new types and functions but I get the following error when trying to subscribe to a <code>.object(path)</code>:</p>
  
  <pre><code>Property 'subscribe' does not exist on type 'AngularFireObject'
  </code></pre>
  
  <p>My code below.</p>
  
  <p><strong>Provider:</strong></p>
  
  <pre><code>getEvent(id: string): AngularFireObject&lt;any&gt; {
      let path = `/events/${id}`;
      return this.af.object(path).valueChanges();
    }
  </code></pre>
  
  <p><strong>Page:</strong></p>
  
  <pre><code>...
  event$: AngularFireObject&lt;any&gt;;
  ...
  
  // Retrieve event's info
  this.event$ = this.eventService.getEvent(this.id);
  
  // Retrieve event's ownership info
  let subscription = this.event$.subscribe(event =&gt; {
    this.owner$ = this.userService.getUserPublicInfo(event.owner);
  });
  </code></pre>
  
  <p>Any idea?</p>