title: Vue v-for data does not get updated on properties change
body: <p>So I render a list of items like</p>
  
  <pre><code>&lt;div v-for="(item, index) in items" :key="item.id"&gt;
    &lt;item :item="item"&gt;&lt;/item&gt;
  &lt;/div&gt;
  </code></pre>
  
  <p>Items looks like this:</p>
  
  <pre><code>items: Array[20]
    0: Object
      sold: false
    1: Object
      sold: true
  </code></pre>
  
  <p>Now I display these items using an overlay. Once an item is marked as "sold" for example, I use VueX to change "items" by watching the VueX data. So I say </p>
  
  <pre><code>items[0].sold = true
  </code></pre>
  
  <p>Now items was changed sucessfully, however, my list does not re-render and thus no change is shown. Any idea why and how to overcome this? One solution would be to watch in every "item" component for a change, but that would mean that I could have hundreds of Vue compontents watching for a change and I guess that would be not a nice solution performance wise.</p>
  
  <p>Thank you!</p>