update gradio

README.md

@@ -35,7 +35,7 @@ Below is an interactive demo for the simulated tabletop manipulation domain, see
 
 
 ## Note
-For GPT-4 model, each inference costs about $0.3. For GPT-3.5 model, each inference costs about $0.03.
+For GPT-4 model, each inference costs about \$0.3. For GPT-3.5 model, each inference costs about \$0.03.
 
 
 ## Acknowledgement