allow symfony/cache ^6 (#415)

Author: fezfez

Diff for: composer.json

@@ -22,7 +22,7 @@
         "psr/http-server-handler": "^1",
         "psr/http-server-middleware": "^1",
         "psr/simple-cache": "^1.0.1",
-        "symfony/cache": "^4.3 | ^5",
+        "symfony/cache": "^4.3 | ^5 | ^6",
         "symfony/expression-language": "^4 | ^5",
         "thecodingmachine/cache-utils": "^1",
         "thecodingmachine/class-explorer": "^1.1.0",