Add PHPUnit 12 support (#26)

Author: keradus

composer.json

@@ -16,7 +16,7 @@
         "php": "^7.0 || ^8.0",
         "ext-dom": "*",
         "ext-libxml": "*",
-        "phpunit/phpunit": "^6.5.14 || ^7.5.20 || ^8.5.41 || ^9.6.22 || ^10.5.45 || ^11.5.7"
+        "phpunit/phpunit": "^6.5.14 || ^7.5.20 || ^8.5.41 || ^9.6.22 || ^10.5.45 || ^11.5.7 || ^12.0.2"
     },
     "autoload": {
         "psr-4": {