Can't load checkpoints for sampling

Hi, thank you for making your code public!

when running the command provided in the "Sampling" section of the README
```
python scripts/sample.py --model transvae --model_ckpt checkpoints/trans4x-256_zinc.ckpt --mols data/zinc_train.txt --sample_mode high_entropy
```

I get
```
_pickle.UnpicklingError: invalid load key, 'v'.
```

any idea how to solve this?

Thanks!