Not compatible with symfony 5

[Tetragramat]

There are two compatibility errors thrown in composer install.

symfony/* 5.0.3
payum/payum-bundle 2.4.0

Fatal error: Declaration of Payum\Bundle\PayumBundle\Profiler\PayumCollector::collect(Symfony\Component\HttpFoundation\Request $request, Symfony\Component\HttpFoundation\Response $response, ?Exception $exception = NULL) must be compatible with Symfony\Component\HttpKernel\DataCollector\DataCollectorInterface::collect(Symfony\Component\HttpFoundation\Request $request, Symfony\Component\HttpFoundation\Response $response, ?Throwable $exception = NULL) in /home/www/app/vendor/payum/payum-bundle/Profiler/PayumCollector.php on line 11

Fatal error: Declaration of Payum\Bundle\PayumBundle\Form\Extension\GatewayFactoriesChoiceTypeExtension::getExtendedTypes() must be compatible with Symfony\Component\Form\FormTypeExtensionInterface::getExtendedTypes(): iterable in /home/www/app/vendor/payum/payum-bundle/Form/Extension/GatewayFactoriesChoiceTypeExtension.php on line 60

Bundle is not tested with symfony 5, so it should be added into travis too.

[Tetragramat]

fixed in #505