update the BAB to the last symfony changes

DependencyInjection/BaseApplicationExtension.php

@@ -17,6 +17,7 @@ use Symfony\Component\DependencyInjection\ContainerBuilder;
 use Symfony\Component\DependencyInjection\Reference;
 use Symfony\Component\DependencyInjection\Definition;
 use Symfony\Component\DependencyInjection\Extension\Extension;
+use Symfony\Component\DependencyInjection\Loader\FileLocator;
 
 use Symfony\Component\Finder\Finder;