chore: provide phpunit options

Author: adhocore

composer.json

@@ -32,7 +32,7 @@
         "adhocore/cron-expr": "^0.1"
     },
     "require-dev": {
-        "phpunit/phpunit": "^6.5",
+        "phpunit/phpunit": "^6.5 || ^7.5",
         "swiftmailer/swiftmailer": "^6.0.0",
         "twig/twig": "^1.3 || ^2.4"
     },