Fix dependency version of symfony 4

Author: francoispluchino

composer.json

@@ -20,7 +20,7 @@
         "php": ">=5.6.0",
         "doctrine/common": "~2.4",
         "symfony/dependency-injection": "~2.3|^3.0|^4.0",
-        "symfony/config": "~2.3|^3.0",
+        "symfony/config": "~2.3|^3.0|^4.0",
         "symfony/http-kernel": "~2.3|^3.0|^4.0",
         "symfony/console": "~2.3|^3.0|^4.0",
         "symfony/monolog-bundle": "~2.3|^3.0|^4.0"