递减key的对应的值，当key不存在时则为默认值，否则在基础上递减整数amount
        :param name: key
        :param amount: 默认值
        :return: 返回递减后的值

def decr(self, name, amount=1):
        """递减key的对应的值，当key不存在时则为默认值，否则在基础上递减整数amount
        :param name: key
        :param amount: 默认值
        :return: 返回递减后的值
        """
        return self.client.decr(name, amount=amount)