Unknown option: .polyfills when trying to add polyfills

[abreitenfeld]

Version

3.1.1

Reproduction link

https://github.com/abreitenfeld/vue-polyfills

Node and OS info

Node v8.11.4
NPM v.5.6.0

Steps to reproduce

1. Create a fresh Vue project via the CLI
2. Extend the babel.config.js with the preset polyfills (according to the CLI documentation)
3. Try to build the project

What is expected?

Build succeeds with the given polyfills

What is actually happening?

Build fails with the error Unknown option: .polyfills

---

I used the example from https://cli.vuejs.org/guide/browser-compatibility.html#polyfills

[haoqunjiang]

module.exports = {
  presets: [
-    '@vue/app', {
+    ['@vue/app', {
      polyfills: [
        'es6.promise',
        'es6.symbol'
      ]
-    }
+    }]
  ]
}