Fixed error

app.py

@@ -128,10 +128,10 @@ chat_interface = gr.ChatInterface(
     ],
 )
 
-with gr.Blocks(css="style.css") as chat_interface:
+with gr.Blocks(css="style.css") as demo:
     gr.Markdown(DESCRIPTION)
     chat_interface.render()
     gr.Markdown(LICENSE)
 
 if __name__ == "__main__":
-    chat_interface.queue(max_size=20).launch()
+    demo.queue(max_size=20).launch()