update pkg installation

Author: jjarvisp

src/pages/[platform]/build-a-backend/add-aws-services/predictions/set-up-predictions/index.mdx

@@ -145,7 +145,7 @@ backend.addOutput({
 To install the Amplify library to use predictions features, run the following commands in your project's root folder:
 
 ```bash title="Terminal" showLineNumbers={false}
-npm add aws-amplify
+npm add aws-amplify @aws-amplify/predictions
 ```
 
 ## Configure the frontend