minor typo on preprocess_util of bert_extraction

[byeongkeonLee]

Hi,

When I run the bert_extraction of SST-2, there is a minor typo that gives an error : 'KeyError: 'sst-2''

In the file:
language/language/bert_extraction/steal_bert_classifier/data_generation/preprocess_util.py

the task_input_indices has some error (task name : 'sst2' which should be 'sst-2')

Could you check this? Thanks.

Best regards,