Update composer.json

Author: andrerom

composer.json

@@ -11,7 +11,7 @@
     ],
     "minimum-stability": "stable",
     "require": {
-        "ezsystems/ezpublish-kernel": "~6.7.7 || ^6.12.1 || ^7.0",
+        "ezsystems/ezpublish-kernel": "~6.7.7@dev || ^6.12.1@dev || ^7.0@dev",
         "friendsofsymfony/http-cache-bundle": "~1.2|^1.3.8",
         "symfony/symfony": "^2.7 | ^3.1"
     },