Update vanilla-typescript.mdx (#10174)

Author: setchy

website/src/pages/docs/guides/vanilla-typescript.mdx

@@ -193,7 +193,7 @@ export async function execute<TResult, TVariables>(
       Accept: 'application/graphql-response+json'
     },
     body: JSON.stringify({
-      query: document,
+      query,
       variables
     })
   })