Fix gunicorn port binding

Dockerfile

@@ -24,4 +24,4 @@ RUN apt-get update && apt-get install -y \
 EXPOSE 7860
 
 # Define the command to run your app using Gunicorn
-CMD exec gunicorn --bind :$PORT app:app
+CMD ["sh", "-c", "gunicorn app:app --bind 0.0.0.0:$PORT"]