_hotkeysJs.default is not a function

When I literally copy and paste the first example in the docs, it just errors out. I changed `F5` to `k` but that's all.

```
import hotkeys from 'hotkeys-js';

hotkeys('k', function(event, handler){
  event.preventDefault()
  alert('you pressed k!')
});
```

This just errors out with `Uncaught TypeError: _hotkeysJs.default is not a function`.

What am I missing here?