chore: 🤖 migrate to vue cli 3

src/index.js

@@ -1,7 +1,8 @@
 /**
  * Created by ayou on 17/7/21.
  */
-exports.VueTreeList = require('./VueTreeList.vue')
-exports.TreeNode = require('./Tree.js').TreeNode
-exports.Tree = require('./Tree.js').Tree
-// exports.Record = require('./Tree.js').Record
+
+import VueTreeList from "./VueTreeList";
+import { Tree, TreeNode } from "./Tree";
+
+export { Tree, TreeNode, VueTreeList };