Require httpkernel for the MonologExtension class

Author: Seldaek

composer.json

@@ -20,6 +20,7 @@
         "symfony/monolog-bridge": "~2.4-dev",
         "symfony/dependency-injection": "~2.2",
         "symfony/config": "~2.2",
+        "symfony/http-kernel": "~2.2",
         "monolog/monolog": "~1.3"
     },
     "require-dev": {