suppress native return type deprecation msg

[PhilETaylor]

Method "Symfony\Component\DependencyInjection\Extension\ExtensionInterface::load()" might add "void" as a native return type declaration in the future. Do the same in implementation "Twig\Extra\TwigExtraBundle\DependencyInjection\TwigExtraExtension" now to avoid errors or add an explicit @return annotation to suppress this message.

[fabpot]

LGTM but this is a read only repository. Can you submit this change on twig/twig instead?

[PhilETaylor]

You would think I would learn my lesson by now - so so sorry. Im an idiot.