Ability to extend options passed to include configFile

For some reason when I have a `babel.config.js` on the project, the `babel()` does not pick up that file, only when I change it to a `.babelrc` it works.

Possibility to add a `configFile` option to specify the path of the `babel` config file to load.

Do we need a PR for this, if not already present?

[Babel-ref](https://babeljs.io/docs/en/options#configfile)
