removed unused option groupsDraggable

lib/timeline/component/ItemSet.js

@@ -34,7 +34,6 @@ function ItemSet(body, options) {
     },
     align: 'auto', // alignment of box items
     stack: true,
-    groupsDraggable: false,
     groupOrderSwap: function(draggedGroup, targetGroup, groups) {
     	var targetOrder = targetGroup.order;
     	targetGroup.order = draggedGroup.order;