[composer] Set dependencies for 2.5.8 release

Author: Łukasz Serwatka

composer.json

@@ -11,7 +11,7 @@
     ],
     "require": {
         "php": "^7.1",
-        "ezsystems/ezpublish-kernel": "^7.0@dev",
+        "ezsystems/ezpublish-kernel": "^7.0",
         "symfony/symfony": "^3.4",
         "jms/translation-bundle": "^1.3"
     },