fix sandbox typo (aws-amplify#7654)

Author: aspittel

src/pages/[platform]/deploy-and-host/sandbox-environments/features/index.mdx

@@ -178,7 +178,7 @@ npx ampx sandbox --outputs-out-dir ./path/to/config --outputs-format ["json", "d
 Alternatively, if you want to generate the config for a branch environment to test against, run the following command in the terminal.
 
 ```bash
-npx ampx generate outputs --app-id <your-amplify-app-id> --branch main --format ["json", "dart"] out-dir ./path/to/config
+npx ampx generate outputs --app-id <your-amplify-app-id> --branch main --format ["json", "dart"] --out-dir ./path/to/config
 ```
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