title: How to concat two observable arrays into a single array?
body: <p>example:</p>
  
  <pre><code>var s1 = Observable.of([1, 2, 3]);
  
  var s2 = Observable.of([4, 5, 6]);
  
  s1.merge(s2).subscribe(val =&gt; {
     console.log(val);
  })
  </code></pre>
  
  <p>I want to get 
  [1,2,3,4,5,6]</p>
  
  <p>instead of </p>
  
  <p>[1,2,3]</p>
  
  <p>[4,5,6]</p>