Support webonyx/graphql-php 15

Fixes #27

Author: PowerKiKi

composer.json

@@ -27,7 +27,7 @@
         "php": "^8.1",
         "ext-json": "*",
         "psr/http-server-middleware": "^1.0",
-        "webonyx/graphql-php": "^14.11"
+        "webonyx/graphql-php": "^15.0"
     },
     "license": "MIT",
     "require-dev": {