Fix index out of bounds error (#4)

- Fix (0810c3b10c0171dd92b3d2494a0e09d8aef5680e)

label_prettify.py

@@ -66,7 +66,7 @@ def seg_prettify(rgb_path, file_name):
 
     for i in np.unique(seg_labels):
         obj_idx_all = np.where(seg_labels == i)
-        obj_idx = random.randint(0, len(obj_idx_all[0] - 1))
+        obj_idx = random.randint(0, len(obj_idx_all[0]) - 1)
         x, y = obj_idx_all[1][obj_idx], obj_idx_all[0][obj_idx]
         obj_name = coco_label_map[int(i * 255)]
         obj_name = obj_name.split(',')[0]