[DoctrineMongoDBBundle] fixed use statement

src/Symfony/Bundle/DoctrineMongoDBBundle/DoctrineMongoDBBundle.php

@@ -4,7 +4,7 @@ namespace Symfony\Bundle\DoctrineMongoDBBundle;
 
 use Symfony\Framework\Bundle\Bundle;
 use Symfony\Components\DependencyInjection\ParameterBag\ParameterBagInterface;
-use Symfony\Components\DependencyInjection\Loader\Loader;
+use Symfony\Components\DependencyInjection\ContainerBuilder;
 use Symfony\Bundle\DoctrineMongoDBBundle\DependencyInjection\MongoDBExtension;
 
 /**