Fixed forward compatibility with PHPStan 0.11.3

Merge pull request phpstan#33 from keichinger/updated-servicesubscrib…

…erinterface

Honor new contracts namespace as-of Symfony 4.2 for ServiceSubscriberInterface

Fixed extension.neon

Merge pull request phpstan#7 from phpstan/type-specifying-extensions

Extensions for ContainerInterface|Controller::has()