title: Reset GitHub login when using composer install
body: <p>I just used composer to install some dependencies for a project. In this project we are using the cartalyst/sentry-social package. To get this I have to use a special GitHub account - but I didn't know that wehen I was using the command about an hour age :/</p>
  
  <p>So now I have entered the wrong GitHub Login Credentials and somehow this gets saved and I didn't figured out how to reset them, so composer/git would ask me again for the login credentials.</p>
  
  <p>So how do I reset this login credentials?</p>