Actually only PHPUnit 7 is required

Author: phpfui

composer.json

@@ -16,7 +16,7 @@
         "rexxars/html-validator": "^2.2"
     },
     "require-dev": {
-        "phpunit/phpunit": "~8.0"
+        "phpunit/phpunit": "~7.0"
     },
     "autoload": {
         "psr-0": {"PHPFUI": "src/"}