rename stuff_names to stuff_classes which is used in Visualizer

Summary:
`stuff_classes` is the correct metadata name that' recognized by visualizer

Pull Request resolved: #2620

Reviewed By: theschnitz

Differential Revision: D26456369

Pulled By: ppwwyyxx

fbshipit-source-id: 157ed4bb0d460d78490916671f8b39ca934181be

Author: patrick-zhang-work

detectron2/data/datasets/cityscapes.py

@@ -315,9 +315,9 @@ def _cityscapes_files_to_dict(files, from_json, to_polygons):
         dicts = load_cityscapes_semantic(args.image_dir, args.gt_dir)
         logger.info("Done loading {} samples.".format(len(dicts)))
 
-        stuff_names = [k.name for k in labels if k.trainId != 255]
+        stuff_classes = [k.name for k in labels if k.trainId != 255]
         stuff_colors = [k.color for k in labels if k.trainId != 255]
-        meta = Metadata().set(stuff_names=stuff_names, stuff_colors=stuff_colors)
+        meta = Metadata().set(stuff_classes=stuff_classes, stuff_colors=stuff_colors)
 
     for d in dicts:
         img = np.array(Image.open(PathManager.open(d["file_name"], "rb")))