Append artificial_done to *args and run parent method.

def add(self, observation, action, reward, terminal, *args):
    """Append artificial_done to *args and run parent method."""
    # If this will be a problem for maintenance, we could probably override
    # DQNAgent.add() method instead.
    artificial_done = self._artificial_done and terminal
    args = list(args)
    args.append(artificial_done)
    return super(_OutOfGraphReplayBuffer, self).add(observation, action, reward,
                                                    terminal, *args)