chore: fix capitalization in documentation.

Author: MarlonJD

Diff for: src/pages/[platform]/build-a-backend/functions/custom-functions/index.mdx

@@ -203,7 +203,7 @@ defineBackend({
 });
 ```
 
-Now when you run `npx ampx sandbox` or deploy your app on Amplify, it will include your Function.
+Now when you run `npx ampx sandbox` or deploy your app on Amplify, it will include your function.
 
 To invoke your function, we recommend adding your [function as a handler for a custom query with your Amplify Data resource](/[platform]/build-a-backend/data/custom-business-logic/). To get started, open your `amplify/data/resource.ts` file and specify a new query in your schema: