Babel configs are ignored

In the ReadMe, there's the following line:

> In order to migrate to optimize-plugin, you'll need to move your babel configuration into a `.babelrc` or `babel.config.js` file ...optimize-plugin only uses your babel configuration when generating _modern_ bundles.

However, both `configFile` and `babelrc` are set to `false`:

https://github.com/developit/optimize-plugin/blob/aefb895750e217be250230f9c0cb78afc00aa4fe/src/worker.js#L59-L61

This should stop any config files from being loaded, AFAIK. Am I misunderstanding something, or are the docs outdated perhaps?