Update Cory Dolphin's Github username in AUTHORS.

Cory Dolphin changed Github usernames from "wcdolphin" to "corydolphin".
Github does not automatically redirect profile links when you change
usernames so his link in the AUTHORS file went to a 404.

https://help.github.com/articles/what-happens-when-i-change-my-username/#changes-that-arent-automatic

AUTHORS.rst

@@ -44,7 +44,7 @@ Patches and Suggestions
 - `Oleg Anashkin <https://github.com/extesy>`_, streaming ``handlers`` functionality
 - `Luis Alberto Santana <https://github.com/jackboot7`_, Added auth_endpoint parameter for cases when the right permissions weren't being shown on authenticate step
 - `Cory Benfield <https://github.com/Lukasa>`_, Fixed issue where Twython was unnecessarily disabling compression
-- `Cory Dolphin <https://github.com/wcdolphin>`_, Added retry_after attribute to TwythonRateLimitError
+- `Cory Dolphin <https://github.com/corydolphin>`_, Added retry_after attribute to TwythonRateLimitError
 - `Natan L <https://github.com/kuyan>`_, Fixed typo in documentation
 - `Cash Costello <https://github.com/cash>`_, Moved tests to use `responsoes`, fixed typos in documentation
 - `Joe Cabrera <https://github.com/greedo>`_, PEP 8 contributions