修复表单构建选择下拉选择控制台报错问题

@@ -573,6 +573,7 @@
 
 <script>
 import { isArray } from 'util'
+import draggable from 'vuedraggable'
 import TreeNodeDialog from './TreeNodeDialog'
 import { isNumberStr } from '@/utils/index'
 import IconsDialog from './IconsDialog'
@@ -595,6 +596,7 @@ const dateTimeFormat = {
 
 export default {
   components: {
+    draggable,
     TreeNodeDialog,
     IconsDialog
   },