Update example so it works with fonts CDNs

First of all, a big thank you! I tried a lot of hacks but butler was the only thing that worked with Rails 4, Heroku, Sumo CDN and a woff font file.

I just experienced some trouble with the default example and I wanted to improve it a bit. If you only add  'Access-Control-Allow-Origin' it seems that browsers will ignore it. You also need to add Access-Control-Allow-Methods and Access-Control-Allow-Headers.

Warm regards,
Ignacio