phpunit update to 7.5

Author: marc-mabe

composer.json

@@ -10,7 +10,7 @@
         "phpstan/phpstan": "^0.10 || ^0.11 || ^0.12"
     },
     "require-dev": {
-        "phpunit/phpunit": "^6.0"
+        "phpunit/phpunit": "^7.5"
     },
     "autoload": {
         "psr-4": {