bump: update to vue-cli@4 (#3028)

babel.config.js

@@ -1,5 +1,14 @@
 module.exports = {
   presets: [
-    '@vue/app'
-  ]
+    // https://github.com/vuejs/vue-cli/tree/master/packages/@vue/babel-preset-app
+    '@vue/cli-plugin-babel/preset'
+  ],
+  'env': {
+    'development': {
+      // babel-plugin-dynamic-import-node plugin only does one thing by converting all import() to require().
+      // This plugin can significantly increase the speed of hot updates, when you have a large number of pages.
+      // https://panjiachen.github.io/vue-element-admin-site/guide/advanced/lazy-loading.html
+      'plugins': ['dynamic-import-node']
+    }
+  }
 }