title: How I can call Observable.complete callback function? It doesn't work
body: <p>In ionic 2, (and angularfire2@4.0.0-rc.0, firebase@3.9.0)
  I tried this code, but complete function doesn't work!</p>
  
  <pre><code>constructor(public af: AngularFireDatabase, ...) { 
    this.temp = af.list('/myTest').subscribe(data =&gt; {
      ...  // my tastks
    }, error =&gt; {
      console.log(error);
    }, () =&gt; {
      console.log("done!");  // I can't see this output!
    });
  }
  </code></pre>
  
  <p>I already tried very many times, but I can't see "done".</p>
  
  <p>In another function, I tried this but the result is same with first.</p>
  
  <pre><code>console.log(this.temp.closed); // false
  this.temp.unsubscribe()
  console.log(this.temp.closed); // true
  </code></pre>
  
  <p>,, What can I do..?</p>