code: public function increment($member, $increment = 1)
      {
          return $this->strToVal(
              $this->redis->zincrby($this->key, $this->valToStr($increment), $this->valToStr($member))
          );
      }
docs: @link https://redis.io/commands/zincrby
  
  @param string|number $member    Score of $member will be incremented.
  @param float|int     $increment Increment the score behind $member by this much.
  
  @return number|string New score behind $member.