updated deps to make it possible to install SE with Symfony 3.0

Author: fabpot

composer.json

@@ -13,7 +13,7 @@
         "doctrine/doctrine-bundle": "~1.4",
         "symfony/assetic-bundle": "~2.3",
         "symfony/swiftmailer-bundle": "~2.3",
-        "symfony/monolog-bundle": "~2.4",
+        "symfony/monolog-bundle": "~2.7@dev",
         "sensio/distribution-bundle": "~5.0@dev",
         "sensio/framework-extra-bundle": "^3.0.2",
         "incenteev/composer-parameter-handler": "~2.0"