Update app.py

app.py

@@ -20,6 +20,8 @@ from detectron2.utils.logger import setup_logger # ????
 from detectron2 import model_zoo
 from detectron2.engine import DefaultPredictor
 from detectron2.config import get_cfg
+from detectron2.utils.visualizer import Visualizer
+from detectron2.data import MetadataCatalog, DatasetCatalog
 
 # ????
 setup_logger()