title: Computed property not updating on props changes
body: <p>I can't get a computed property to update, when a nested property in a passed prop object is changed.</p>
  
  <p><strong>this.favourite</strong> is passed via props, but the computed property is not updating when <strong>this.favourite.selectedChoices.second.id</strong> and <strong>this.favourite.selectedChoices.first.id</strong> is changed.</p>
  
  <p>Any ideas of how to make this reactive?</p>
  
  <p>Here's the computed property:</p>
  
  <pre><code>isDisabled() {
    const hasMultipleChoices = this.favourite.choices.length
      ? this.favourite.choices[0].value.some(value =&gt; value.choices.length) : 
      false;
  
    if (hasMultipleChoices &amp;&amp; !this.favourite.selectedChoices.second.id) {
      return true;
    } else if (this.favourite.choices.length &amp;&amp; !this.favourite.selectedChoices.first.id) {
      return true;
    }
  
    return false;
  }
  </code></pre>