title: Angular-Formly Nested Model Not Updating
body: <p>I am having an interesting issue with angular-formly. I am attempting to use the 'model' tag as shown below because my model is not flat.</p>
  
  <pre><code>{
      'key': 'last',
      'model': 'model.name',
      'templateOptions: {}
  } 
  </code></pre>
  
  <p>However, I cannot update the model in a clean manner. Simply replacing model or even model.name with a matching model that contains the updated value does not cause the model to update the view. </p>
  
  <pre><code>var newModel = {
      name: {
          first: 'Gandalf',
          last: 'The White'
      }
  };
  self.model = {
      name: {
          first: 'Gandalf',
          last: 'The Grey'
      }
  };
  function setNewLastName() {
      self.model = newModel;
  }
  setNewLastName();
  </code></pre>
  
  <p>However if I drill down to the specific property, it works as expected.</p>
  
  <pre><code>self.model.name.last = self.newModel.name.last;
  </code></pre>
  
  <p>Here is a link to a JSBin where the value updates using the drill-down method immediately above.
  <a href="http://jsbin.com/jewapi/edit?js,console,output" rel="nofollow">Drill-down JSBin</a></p>
  
  <p>Another JSBin that attempts to update the model by assigning a new model that does not update.
  <a href="http://jsbin.com/newuri/edit?js,console,output" rel="nofollow">Assign Model JSBin</a></p>
  
  <p>Has anyone ran into this issue or can you see where I'm doing something wrong?</p>