code: public function initRed($channel, array $config)
      {
          try {
              switch ($channel) {
                  case Config::ALI_RED:
                      $this->red = new AliRed($config);
                      break;
                  case Config::WX_RED:
                      $this->red = new WxRed($config);
                      break;
                  default:
                      throw new PayException('当前仅支持：ALI WEIXIN两个常量');
              }
          } catch (PayException $e) {
              throw $e;
          }
      }
docs: 设置对应的发送渠道
  @param string $channel 退款渠道
  - @see Config
  
  @param array $config 配置文件
  @throws PayException
  @author IT