Upgrade to PHPUnit 8

Author: zlikavac32

composer.json

@@ -16,7 +16,7 @@
         "ext-json": "*"
     },
     "require-dev": {
-        "phpunit/phpunit": "^7.0",
+        "phpunit/phpunit": "^8.0",
         "phpspec/phpspec": "^5.1"
     },
     "autoload": {