Allow PHPUnit 9

Author: MGatner

composer.json

@@ -19,7 +19,7 @@
 		"fakerphp/faker": "^1.9",
 		"mikey179/vfsstream": "^1.6",
 		"phpstan/phpstan": "^0.12",
-		"phpunit/phpunit": "^8.5",
+		"phpunit/phpunit": "^8.5 || ^9.1",
 		"predis/predis": "^1.1",
 		"rector/rector": "^0.8",
 		"squizlabs/php_codesniffer": "^3.3"