vue项目如何引入babel-polyfill 
babel-pollyfill 官方说的是：
```
With webpack.config.js, add babel-polyfill to your entry array:
```
```
With webpack.config.js, add babel-polyfill to your entry array:
module.exports = {
  entry: ["babel-polyfill", "./app/js"]
};
```
但是项目没有webpack.config.js， 倒是有 build/webpack.base.conf.js。 但是里面的结构为：
```
module.exports = {
  entry: {
    app: './src/main.js'
  },
  output: {
    path: config.build.assetsRoot,
    filename: '[name].js',
    publicPath: process.env.NODE_ENV === 'production'
      ? config.build.assetsPublicPath
      : config.dev.assetsPublicPath
  }
...
```
entry: ["babel-polyfill", "./app/js"]  该怎么加进去呢？
main.js 里面引入
```
import 'babel-polyfill'
```
webpack.base.conf.js 替换到entry部分
```
  entry: {
    // app: './src/main.js'
    app: ["babel-polyfill", "./src/main.js"]
  },
```
注意：多试一下，清空缓存，多试试，我也是捣鼓捣鼓才可以的