Fix several deprecation notices

[XWB]

This fixes several deprecation notices:

Method "Twig\Extension\ExtensionInterface::getFunctions()" might add "array" as a native return type declaration in the future. Do the same in implementation "FOS\HttpCacheBundle\Twig\CacheTagExtension" now to avoid errors or add an explicit @return annotation to suppress this message.

Method "Symfony\Component\EventDispatcher\EventSubscriberInterface::getSubscribedEvents()" might add "array" as a native return type declaration in the future. Do the same in implementation "FOS\HttpCacheBundle\EventListener\CacheControlListener" now to avoid errors or add an explicit @return annotation to suppress this message.

Method "Symfony\Component\Config\Definition\ConfigurationInterface::getConfigTreeBuilder()" might add "TreeBuilder" as a native return type declaration in the future. Do the same in implementation "FOS\HttpCacheBundle\DependencyInjection\Configuration" now to avoid errors or add an explicit @return annotation to suppress this message.

Method "Symfony\Component\DependencyInjection\Extension\ConfigurationExtensionInterface::getConfiguration()" might add "?ConfigurationInterface" as a native return type declaration in the future. Do the same in implementation "FOS\HttpCacheBundle\DependencyInjection\FOSHttpCacheExtension" now to avoid errors or add an explicit @return annotation to suppress this message. 

User Deprecated: Method "Sensio\Bundle\FrameworkExtraBundle\Configuration\ConfigurationInterface::getAliasName()" might add "string" as a native return type declaration in the future. Do the same in implementation "FOS\HttpCacheBundle\Configuration\Tag" now to avoid errors or add an explicit @return annotation to suppress this message. 

User Deprecated: Method "Sensio\Bundle\FrameworkExtraBundle\Configuration\ConfigurationInterface::allowArray()" might add "bool" as a native return type declaration in the future. Do the same in implementation "FOS\HttpCacheBundle\Configuration\Tag" now to avoid errors or add an explicit @return annotation to suppress this message. 

[dbu]

thanks, looks good. i added two suggestions, can you check if you agree with these?

[XWB]

@dbu Done :)

[dbu]

thank you!