Upgrade phpuit to v7.4

Author: slavcodev

composer.json

@@ -16,7 +16,7 @@
     "ext-json": "*"
   },
   "require-dev": {
-    "phpunit/phpunit": "~6.4.4",
+    "phpunit/phpunit": "^7.4",
     "scrutinizer/ocular": "~1.1"
   },
   "autoload": {