docs: typo in command build

Signed-off-by: David Dal Busco <david.dalbusco@outlook.com>

Author: peterpeterparker

docs/guides/rust.mdx

@@ -28,7 +28,7 @@ Now, your local development environment is up and running, ready for you to star
 Once you're ready to see your changes in action, compile your code:
 
 ```bash
-juno emulator build
+juno functions build
 ```
 
 Changes are detected and automatically deployed, allowing you to test your custom code locally almost immediately.