Fix to issue #100: 500 error when logging in

self.token on 
https://github.com/codetriage/codetriage/blob/master/app/models/user.rb#L84

it was throwing this error message on development.rb:
NoMethodError (undefined method `token' for #<Class:0x007f83fd2feff8>):
  app/models/user.rb:84:in `find_for_github_oauth'
  app/controllers/users/omniauth_callbacks_controller.rb:4:in `github'