src/Pay.php
public function gateway($gateway = 'web')
    {
        if (!isset($this->drivers)) {
            throw new InvalidArgumentException('Driver is not defined.');
        }
        return $this->gateways = $this->createGateway($gateway);
    }
public function gateway($gateway = 'web')
    {
        if (!isset($this->drivers)) {
            throw new InvalidArgumentException('Driver is not defined.');
        }
        return $this->gateways = $this->createGateway($gateway);
    }
指定操作网关
@param string $gateway
@return GatewayInterface