Updating for MaxCDN

Update for [MaxCDN](http://www.maxcdn.com/) to automatically purge CDN cache on push event.

##### Notes:
1. It would be my preference to display Github's web hook IP block listed under the hook key at https://api.github.com/meta. That said, there was no clear location in which to add a display helper for use with in docs files (i.e. `docs/maxcdn`), nor is there a method to test such a helper that I'm aware of.
2. All gem updates in this pull request were automatically updated when running `./script/bootstrap`, only the additions of `curb`, `curb-fu`, and `maxcdn` are required for the intended changes.
3. The update to `i18n` added a deprecation message of "**_[deprecated] I18n.enforce_available_locales will default to true in the future. If you really want to skip validation of your locale you can set I18n.enforce_available_locales = false to avoid this message._**", as I mentioned above, this update was done by `./script/bootstrap` and not purposefully as part of this pull request.