Allow Symfony 6 (#96)

Author: barryvdh

composer.json

@@ -13,8 +13,8 @@
     ],
     "require": {
         "php": "^7.0|^8.0",
-        "symfony/http-foundation": "~2.7|~3.0|~4.0|~5.0",
-        "symfony/http-kernel": "~2.7|~3.0|~4.0|~5.0"
+        "symfony/http-foundation": "~2.7|~3.0|~4.0|~5.0|~6.0",
+        "symfony/http-kernel": "~2.7|~3.0|~4.0|~5.0|~6.0"
     },
     "require-dev": {
         "phpunit/phpunit": "^6|^7|^8|^9",