Fix invalid usage of useMemo() in docs (#4281)

Summary:
Hello relay!

While I was looking for a guide for Relay subscription, I think I found a kind of typo in guided-tour docs.

Any feedbacks are welcome.

Thanks!

Pull Request resolved: #4281

Reviewed By: voideanvalue

Differential Revision: D45678724

Pulled By: captbaritone

fbshipit-source-id: ccc06d1695bfe1b2c247c76db6bbf13c9439dc19

website/docs/guided-tour/updating-data/graphql-subscriptions.md

@@ -100,7 +100,7 @@ const {useMemo} = require('React');
 function useFeedbackSubscription(
   input: FeedbackLikeSubscribeData,
 ) {
-  const config = useMemo({
+  const config = useMemo(() => ({
     subscription: graphql`
       subscription FeedbackLikeSubscription(
         $input: FeedbackLikeSubscribeData!
@@ -113,7 +113,7 @@ function useFeedbackSubscription(
       }
     `,
     variables: {input},
-  }, [input])
+  }), [input]);
 
   return useSubscription(config);
 }