title: konvajs: item location not change after drag and drop
body: <p>So with konva.js I have a group with two Text items. I made the group <code>draggable</code>.  After dragging it though I printed out <code>x</code> and <code>y</code> for the Text but it never changed:</p>
  
  <pre><code>group.on('dragend', function() {
      var group = this;
      var t = group.findOne('Text');
      console.log(t.x(), t.y());
  });
  </code></pre>
  
  <p>The rest of the code is exactly the same as <code>Konva Text Demo</code></p>