'Check to see if ``username`` is a collaborator on this repository.
:param username: (required), login for the user
:type username: str or :class:`User <github3.users.User>`
:returns: bool -- True if successful, False otherwise'

@requires_auth
def is_collaborator(self, username):

    if (not username):
        return False
    url = self._build_url(u'collaborators', str(username), base_url=self._api)
    return self._boolean(self._get(url), 204, 404)
