Fixed MIME type of mp3 for #223

`(new Audio()).canPlayType('audio/mpeg')`
Works on Chrome 36.0.1985.125, Firefox 30.0 and IE11

References: [Chromium_issues_386073#c11](https://code.google.com/p/chromium/issues/detail?id=386073#c11), [RFC_3003](http://tools.ietf.org/html/rfc3003), [Video_type_parameters#MPEG](http://wiki.whatwg.org/wiki/Video_type_parameters#MPEG)