title: Ember.merge does not trigger property change
body: <p>I'm manipulating an array using Ember.merge. However, this does not seem to trigger a change in the template where I display something if the array is present. This seems to work when I use array.pushObjects. Just wondering if this is desired behavior. Related twiddle: 
  <a href="https://ember-twiddle.com/9782f55c16c052851965055fd92c1bf9" rel="nofollow">https://ember-twiddle.com/9782f55c16c052851965055fd92c1bf9</a></p>