Fixed incorrect example usage of update_user()

Also would recommend that the the :bio option not be shown as this is a essentially deprecated feature.  Its not shown on GitHub.com UI and has been mentioned to be deprecated: https://github.com/github/github-services/issues/503#issuecomment-12654988
Merge pull request #387 from StephenOTT/patch-4

Fixed incorrect example usage of update_user()