title: Update an item in the list
body: <p>I'm a beginner on knockout.</p>
  
  <p>I made this page:</p>
  
  <p><a href="http://jsfiddle.net/LhTx4/" rel="nofollow">http://jsfiddle.net/LhTx4/</a></p>
  
  <p>I would like to update only the item that comes back from the sellIt function.</p>
  
  <p>How can I do that?</p>