feat: fix deprecation for Extension (#78)

Co-authored-by: Christopher Georg <[email protected]>

src/DependencyInjection/CalendarExtension.php

@@ -6,8 +6,8 @@
 
 use Symfony\Component\Config\FileLocator;
 use Symfony\Component\DependencyInjection\ContainerBuilder;
+use Symfony\Component\DependencyInjection\Extension\Extension;
 use Symfony\Component\DependencyInjection\Loader\YamlFileLoader;
-use Symfony\Component\HttpKernel\DependencyInjection\Extension;
 
 /**
  * This is the class that loads and manages your bundle configuration.