Allow symfony 6 packages (#43)

Author: FabianSchmick

composer.json

@@ -23,9 +23,9 @@
     "require": {
         "php": ">=7.1",
         "ext-json": "*",
-        "symfony/config": "~3.0|~4.0|~5.0",
-        "symfony/dependency-injection": "~3.0|~4.0|~5.0",
-        "symfony/http-kernel": "~3.0|~4.0|~5.0",
+        "symfony/config": "~3.0|~4.0|~5.0|~6.0",
+        "symfony/dependency-injection": "~3.0|~4.0|~5.0|~6.0",
+        "symfony/http-kernel": "~3.0|~4.0|~5.0|~6.0",
         "twig/twig": "^1.34|^2.0|^3.0"
     },
     "require-dev": {