Update Facebook authorize URL to fix broken authorization

Today Facebook update their platform with major OAuth breaking change, and affected several website including MySpace, Pinterest and StackOverflow.

According to the bug ticket on Facebook Developers platform:
[Enabling Facebook Breaking Changes Feb 2013 Does Not Work](https://developers.facebook.com/bugs/207955409343730), Øyvind Sean Kinsey, Software Engineer at Facebook, responded:

> Please note that the graph.facebook.com/oauth/authorize endpoint is deprecated in favor of www.facebook.com/dialog/oauth and that this should always be used to avoid issues.Today Facebook update their OAuth