title: Listen to changes from nested model attributes
body: <p>I have a model attribute which is an object:</p>
  
  <pre><code>name : "testing",
  orderCondition: {
    minOrderAmount: 20, 
    deliveryCostRequire: "MIN_ORDER_AMOUNT", 
    deliveryCostAmount: 5.55
  }
  </code></pre>
  
  <p>When I use <code>listenTo</code> like this, the <code>render</code> function is not called</p>
  
  <pre><code>this.listenTo(this.model, "change:orderCondition", this.render); // NO FIRING
  </code></pre>
  
  <p>But when I use <code>listenTo</code> on other attributes, it works.</p>
  
  <pre><code>this.listenTo(this.model, "change:name", this.render); // FIRING
  </code></pre>
  
  <p>Why <code>listenTo</code> doesn't see changes in nested objects but see  them in simple attributes?</p>