setting port from environment variable

app.py

@@ -486,6 +486,7 @@ def main():
              )
 
     # launch
+    args.port = int(os.environ.get('PORT', 7860))  # default port is 7860 if PORT env var is not set
     demo.launch(server_port=args.port, server_name=args.host, share=args.share)