Toxicity Measurement Should Allow GPU Usage

The toxicity measurement is based on BERT models in HuggingFace, and thus, should be able to utilize GPUs at inference time if a user wants. Suggesting to add the following line to `_download_and_prepare`:

`device = torch.device("cuda:0") if torch.cuda.is_available() else torch.device("cpu")`

And then add `device=device` param to `pipeline`.