code: func (r *Redis) Set(key string, val interface{}, timeout time.Duration) (err error) {
  	conn := r.conn.Get()
  	defer conn.Close()
  
  	var data []byte
  	if data, err = json.Marshal(val); err != nil {
  		return
  	}
  
  	_, err = conn.Do("SETEX", key, int64(timeout/time.Second), data)
  
  	return
  }
docs: //Set 设置一个值