Require PHP8 and phpunit 9

Author: Christoph Singer

composer.json

@@ -4,13 +4,13 @@
     "type":"library",
     "license":"MIT",
     "require": {
-        "php": ">=5.4",
+        "php": ">=8",
         "mrclay/jsmin-php": "^2.3",
         "tubalmartin/cssmin": "^4",
         "symfony/options-resolver": ">=2.3"
     },
     "require-dev": {
-        "phpunit/phpunit": "^4|^5|^6|^7"
+        "phpunit/phpunit": "^9"
     },
     "autoload":{
         "psr-4":{