Dragging clones the source element creating a duplicate CSS ID

[vanboom]

When a sortable element is picked up (dragged), the "ghost" element created has the same CSS ID in the DOM as the original element.

To Reproduce
Debugging is required to detect this...

1. Start gragging an element.
2. Notice the cloneEl element created within the _onDragStart function will have the same ID as the dragEl.

Expected behavior
A duplicate CSS ID should not be created.

Information
Easy to fix -- will submit a PR.