fixing collada examples on github

Hi @mrdoob ,

This is broken on the GitHub site ([link to sample](http://threejs.org/examples/#webgl_loader_collada_skinning) issue) because of the case of the DAE file case, as it can be seen on this screenshot:

![](https://www.evernote.com/shard/s260/sh/9a5a5945-5804-4732-a190-fe795131cea0/7b8ed5d61baf324e9fe59550725058a0/deep/0/three.js%20-%20examples%20and%20Desktop.png)

This is the wrongly cased file on master: https://github.com/mrdoob/three.js/commits/master/examples/models/collada/avatar.DAE

It works fine on macs as the file system is case preserving, but case insensitive, so local web requests work just fine.

Cheers,
- Daniel