KeyError when using Roberta

[mxnno]

If you want to use --model roberta, there will be a KeyError in the class BaseInstance in dataset,py, because the Roberta Tokenizer does not have token_type_ids.
Small workaround for single input sentences:
Replace self.segments = embed_data['token_type_ids'] with `self.segments = [0] * len(embed_data['input_ids'])``