Rename GitHub#update_user to GitHub#update_me

GitHub#update_me only uses one API request now. User#update has been
removed. Removed old tests. Add new unit test.

Closes #319
Record integration test for GitHub#update_me
Update release notes with mention of GitHub#update_me
Merge pull request #323 from sigmavirus24/bug/319

Rename GitHub#update_user to GitHub#update_me