feat(tests): upgrade PHPUnit to the 9.x series

Author: ramsey

composer.json

@@ -14,8 +14,8 @@
     "symfony/console": "^4.0"
   },
   "require-dev": {
-    "phpunit/phpunit": "^7.0",
-    "php-mock/php-mock-prophecy": "^0.0.2"
+    "phpunit/phpunit": "^9",
+    "phpspec/prophecy-phpunit": "^2.0"
   },
   "license": "MIT",
   "authors": [