Revoke user token
        Erases user token on file forcing them to re-login and obtain a new one.
        :param user_id: int
        :return:

def revoke_user_token(self, user_id):
        """
        Revoke user token
        Erases user token on file forcing them to re-login and obtain a new one.
        :param user_id: int
        :return:
        """
        user = self.get(user_id)
        user._token = None
        self.save(user)