download_url still used despite deprication in latest torchaudio release

The latest torchaudio has deprecated the 'download_url' method and removed it from torchaudio.datasets.utils. According to https://github.com/pytorch/audio/issues/1883 it should be replaced with with `torch.hub.download_url_to_file` and [torchaudio.datasets.utils.validate_file](https://github.com/pytorch/audio/blob/e885204ea0d343b8bddd7e829b9e7b29e7c5a9bb/torchaudio/datasets/utils.py#L116). 