code: public Long zadd(Object key, double score, Object member) {
  		Jedis jedis = getJedis();
  		try {
  			return jedis.zadd(keyToBytes(key), score, valueToBytes(member));
  		}
  		finally {close(jedis);}
  	}
docs: 将一个或多个 member 元素及其 score 值加入到有序集 key 当中。
  如果某个 member 已经是有序集的成员，那么更新这个 member 的 score 值，
  并通过重新插入这个 member 元素，来保证该 member 在正确的位置上。