refactor: add phpunit to require

Refs: #18

Author: DenTray

composer.json

@@ -17,7 +17,8 @@
   ],
   "require": {
     "php": ">=7.1.0",
-    "laravel/framework": ">=5.3.0"
+    "laravel/framework": ">=5.3.0",
+    "phpunit/phpunit": ">=7.0|<=10.*"
   },
   "autoload": {
     "psr-4": {