Update MonologExtension.php

Author: dquerioux

DependencyInjection/MonologExtension.php

@@ -618,7 +618,7 @@ private function buildHandler(ContainerBuilder $container, $name, array $handler
             $definition->setArguments(array(
                 $handler['level'],
                 $handler['bubble'],
-                $handler['app_name'],
+                $handler['app-name'],
             ));
             break;