code: protected function createGateway($gateway)
      {
          if (!file_exists(__DIR__ . '/Gateways/' . ucfirst($this->drivers) . '/' . ucfirst($gateway) . 'Gateway.php')) {
              throw new InvalidArgumentException("Gateway [$gateway] is not supported.");
          }
          $gateway = __NAMESPACE__ . '\\Gateways\\' . ucfirst($this->drivers) . '\\' . ucfirst($gateway) . 'Gateway';
          return new $gateway($this->config->get($this->drivers));
      }
docs: 创建操作网关
  @param string $gateway
  @return mixed