[ISSUE-3] more explicit version on one step before Frontend Schlitten fährt

Author: ElectricMaxxx

composer.json

@@ -17,7 +17,7 @@
     ],
     "require": {
         "php": "^7.1",
-        "symfony/framework-bundle": "^2.8 || ^3.3 || ^4.0",
+        "symfony/framework-bundle": "^2.8.18 || ^3.2.5 || ^4.0",
         "sonata-project/doctrine-phpcr-admin-bundle": "^2.2",
         "sonata-project/admin-bundle": "^3.6.0",
         "symfony-cmf/tree-browser-bundle": "^2.0"