Update app.py

app.py

@@ -66,12 +66,12 @@ def main():
             cmd = cmd + " --use-natural"
 
         out_dir = (save_dir / Path(img_path).name).with_suffix("")
-        mesh_path = out_dir / "us.ply"
+        mesh_path = out_dir / "us.obj"
 
         if not mesh_path.is_file():
             subprocess.call(cmd.split())
 
-        return mesh_path
+        return str(mesh_path)
 
     examples = []
     for img_path in Path("./data/images").glob("*"):