Merge pull request #282 from dvdbot/patch-1

this._sortable undefined in beforeDestroy Hook

Author: David-Desmaisons

src/vuedraggable.js

@@ -151,7 +151,7 @@
       },
 
       beforeDestroy() {
-        this._sortable.destroy()
+        if(this._sortable !== undefined) this._sortable.destroy();
       },
 
       computed: {