Update dependency phpunit/phpunit to v7.5.11

Author: renovate-bot

composer.json

@@ -17,7 +17,7 @@
         "psr/http-message": "^1.0"
     },
     "require-dev": {
-        "phpunit/phpunit": "7.5.6",
+        "phpunit/phpunit": "7.5.11",
         "phpunit/php-code-coverage": "6.1.4",
         "sunrise/http-factory": "1.0.6"
     },