Added conditional statement whether dragged element should be dropped

Author: Luca Dalpra

Sortable.js

@@ -2476,7 +2476,9 @@
  el.removeAttribute('draggable');
  });
 
- this._onDrop();
+ if (el === rootEl) {
+ this._onDrop();
+ }
 
  this._disableDelayedDragEvents();