Update howler to 1.1.25.

[Changelog](https://github.com/goldfire/howler.js/blob/c39e1e3544613b77ab419d4c769b108edc028925/CHANGELOG.md)

## 1.1.25 (July 29, 2014)
- `ADDED`: The `AudioContext` is now available on the global `Howler` object (thanks Matt DesLauriers).
- `FIXED`: When falling back to HTML5 Audio due to XHR error, delete cache for source file to prevent multi-playback issues.

## 1.1.24 (July 20, 2014)
- `FIXED`: Improved performance of loading files using data URIs (thanks Rob Wu).
- `FIXED`: Data URIs now work with Web Audio API (thanks Rob Wu).
- `FIXED`: Omitting the second parameter of the `off` method now correctly clears all events by that name (thanks Gabriel Munteanu).
- `FIXED`: Fire `end` event when unloading playing sounds.
- `FIXED`: Small error fix in iOS check.

## 1.1.23 (July 2, 2014)
- `FIXED`: Playing multiple sprites rapdily with HTML5 Audio cause the sprite to break due to a v1.1.22 update.
- `FIXED`: Don't run the iOS test if there is no audio context, which prevents a breaking error.