fix(): update phpunit 7 to 8

Author: Samuel Gomis

composer.json

@@ -32,7 +32,7 @@
   },
   "require-dev": {
     "friendsofphp/php-cs-fixer": "^3.5",
-    "phpunit/phpunit": "^7.0",
+    "phpunit/phpunit": "^8.0",
     "phpspec/phpspec": "^7.1",
     "symfony/yaml": "^4.2",
     "donatj/mock-webserver": "^2.0",