Use async/await in vue files

lib/build/webpack/vue-loader.config.js

@@ -4,6 +4,10 @@ const { defaults } = require('lodash')
 
 module.exports = function () {
   let babelOptions = JSON.stringify(defaults(this.options.build.babel, {
+    plugins: [
+      'transform-async-to-generator',
+      'transform-runtime'
+    ],
     presets: [
       ['es2015', { modules: false }],
       'stage-2'