Support PHPUnit 9 in this branch too.

Author: Naktibalda

composer.json

@@ -19,7 +19,7 @@
 
     "require": {
         "php": ">=7.2.0 <8.0",
-        "phpunit/phpunit": "^8.4"
+        "phpunit/phpunit": "^8.4 | ^9.0"
     },
     "autoload":{
         "classmap": ["src/"]