Nick change

async def _on_nick(self, msg: IrcMessage) -> None:
        """
        Nick change
        """
        user = self.get_user(msg.prefix)
        old_nick = user.name
        del self._users[old_nick]
        user.name = msg.rest
        if old_nick == self.nick:
            # (Forced?) Nick change for ourself
            self.nick = user.name
        self._users[user.name] = user
        self._log.info("{} changed their nick from {} to {}".format(user, old_nick, user.name))