Issue: Possibly wrong documentation about labels in BERT classifier
Possibly also elsewhere, but when discussing the proper format of labels for BERT classification, the documentation states the following:

https://github.com/huggingface/pytorch-transformers/blob/44dd941efb602433b7edc29612cbdd0a03bf14dc/pytorch_transformers/modeling_bert.py#L935

However, shouldn't it be `[0, ..., config.num_labels - 1]`? After all, [`CrossEntropyLoss`](https://pytorch.org/docs/stable/nn.html#crossentropyloss) is being used here. 
Indeed. @LysandreJik I think it should be `Indices should be in ``[0, ..., config.num_labels-1]`` for classification or torch.floats for regression`, what do you think? 