Update gradio-server.mdx

no need `cp server.py app.py` as file name already is `app.py`.

Author: karenwky

units/en/unit2/gradio-server.mdx

@@ -167,7 +167,6 @@ textblob
 
 3. Push your code to the Space:
 ```bash
-cp server.py app.py
 git init
 git add app.py requirements.txt
 git commit -m "Initial commit"