Update phpunit

Author: odan

composer.json

@@ -11,7 +11,7 @@
         "php": ">=7.1"
     },
     "require-dev": {
-        "phpunit/phpunit": "^6.0|^7.0",
+        "phpunit/phpunit": "^7.0",
         "phpstan/phpstan-shim": "^0.11"
     },
     "scripts": {