Fix CoreBundle dependency

composer.json

@@ -33,7 +33,7 @@
         "sonata-project/jquery-bundle": "1.8.*",
         "sonata-project/exporter": "1.*",
         "sonata-project/block-bundle": "~2.2,>=2.2.7",
-        "sonata-project/core-bundle": "~2.2",
+        "sonata-project/core-bundle": "~2.2@dev",
         "doctrine/common": "~2.2"
     },
     "require-dev": {