Bump doctrine commons requirement

As of 2.4, the inflector has it's own namespace.

composer.json

@@ -33,7 +33,7 @@
         "sonata-project/exporter": "~1.0",
         "sonata-project/block-bundle": "~2.2,>=2.2.7",
         "sonata-project/core-bundle": "~2.2,>=2.2.1",
-        "doctrine/common": "~2.2",
+        "doctrine/common": "~2.4",
         "knplabs/knp-menu-bundle": ">=1.1.0,<3.0.0",
         "knplabs/knp-menu": ">=1.1.0,<3.0.0"
     },