TypeError: must start with number, buffer, array or string

👋 I've upgraded to 0.1.1 and now I get the following error using [this config](https://github.com/gpbl/isomorphic500/blob/master/webpack/prod.config.js). I'm on node 4. 

```
$ webpack --stats --config ./webpack/prod.config.js

buffer.js:167
  throw new TypeError('must start with number, buffer, array or string');
  ^
```

Am I missing something?
