Error while running colab notebook

Hello, 

When I try to compile the model using your colab notebook, I get the following error: 

```
The checkpoint state_dict contains keys that are not used by the model:
  pixel_mean
  pixel_std
  proposal_generator.anchor_generator.cell_anchors.{0, 1, 2, 3, 4}
```

Any idea what could be going wrong? Cheers!