Update index.mdx (#7253)

Modified link for "Serverless APIs" points to the correct URL.

Author: abhisuma02

src/pages/[platform]/start/getting-started/nextsteps/index.mdx

@@ -65,7 +65,7 @@ What next? Here are some things to add to your app:
 
 - [Authentication](/[platform]/build-a-backend/auth/set-up-auth/)
 - [User File Storage](/[platform]/build-a-backend/storage/set-up-storage/)
-- [Serverless APIs](/[platform]/build-a-backend/storage/set-up-storage/)
+- [Serverless APIs](/[platform]/build-a-backend/graphqlapi/set-up-graphql-api/)
 - [Analytics](/[platform]/build-a-backend/more-features/analytics/set-up-analytics/)
 - [AI/ML](/[platform]/build-a-backend/more-features/predictions/set-up-predictions/)
 - [PubSub](/[platform]/build-a-backend/more-features/pubsub/set-up-pubsub/)
@@ -75,7 +75,7 @@ What next? Here are some things to add to your app:
 
 - [Authentication](/[platform]/build-a-backend/auth/set-up-auth/)
 - [User File Storage](/[platform]/build-a-backend/storage/set-up-storage/)
-- [Serverless APIs](/[platform]/build-a-backend/storage/set-up-storage/)
+- [Serverless APIs](/[platform]/build-a-backend/graphqlapi/set-up-graphql-api/)
 - [Analytics](/[platform]/build-a-backend/more-features/analytics/set-up-analytics/)
 - [In-App Messaging](/[platform]/build-a-backend/more-features/in-app-messaging/)
 - [Push Notifications](/[platform]/build-a-backend/push-notifications/set-up-push-notifications/)