Allow symfony 6 packages (#9)

Author: FabianSchmick

composer.json

@@ -14,12 +14,12 @@
 
     "require": {
         "php": "7.2.*|7.3.*|7.4.*|8.0.*|8.1.*",
-        "symfony/config": "^3.4|^4.0|^5.0",
-        "symfony/dependency-injection": "^3.4|^4.0|^5.0",
-        "symfony/event-dispatcher": "^3.4|^4.0|^5.0",
-        "symfony/http-foundation": "^4.3|^5.0",
-        "symfony/http-kernel": "^4.3|^5.0",
-        "symfony/routing": "^3.4|^4.0|^5.0"
+        "symfony/config": "^3.4|^4.0|^5.0|^6.0",
+        "symfony/dependency-injection": "^3.4|^4.0|^5.0|^6.0",
+        "symfony/event-dispatcher": "^3.4|^4.0|^5.0|^6.0",
+        "symfony/http-foundation": "^4.3|^5.0|^6.0",
+        "symfony/http-kernel": "^4.3|^5.0|^6.0",
+        "symfony/routing": "^3.4|^4.0|^5.0|^6.0"
     },
 
     "require-dev": {