Bugfix: <DraggableCore> wasn't calling back with DOM node

Author: STRML

lib/utils/positionFns.es6

@@ -78,15 +78,15 @@ export function createCoreData(draggable: DraggableCore, x: number, y: number):
   if (isStart) {
     // If this is our first move, use the x and y as last coords.
     return {
-      node: ReactDOM.findDOMNode(this),
+      node: ReactDOM.findDOMNode(draggable),
       deltaX: 0, deltaY: 0,
       lastX: x, lastY: y,
       x: x, y: y
     };
   } else {
     // Otherwise calculate proper values.
     return {
-      node: ReactDOM.findDOMNode(this),
+      node: ReactDOM.findDOMNode(draggable),
       deltaX: x - state.lastX, deltaY: y - state.lastY,
       lastX: state.lastX, lastY: state.lastY,
       x: x, y: y