title: Why Observable.zip doesn't call finallyDo?
body: <p>Simply, I have this code. But finallyDo is never called for Observable.zip ...Why?</p>
  
  <pre><code>Observable&lt;Integer&gt; observable1 = Observable.just(1);
  Observable&lt;Integer&gt; observable2 = Observable.just(2);
  Observable&lt;Double&gt; observable = Observable.zip(
      observable1,
      observable2, 
      (Func2)(t1,t2)-&gt;{return (double)t1/(double)t2;}
  );
  observable.finallyDo(()-&gt; {Log.e("","Done");});//is never called;
  observable.subscribe(observer);
  </code></pre>