filtering for BPM doesn't work

I am not entirely sure if this is with the soundcloud API or this library but I found that

```
SC.get('/tracks', { q: searchQuery, bpm: { from: 100 }, streamable: true, limit: 10}, (err, tracks) => {

}
```

Does not seem to work, the bpm field remains null for any and all of the results.
Is this me misunderstanding the API or could this be an issue with the library?
