sentencepiece dependency must be a specific version. 
# 🐛 Bug

## Information
Now the `sentencepiece` library has upgraded to `0.1.92` version which is incompatible with `transformers==2.8.0`.

## Error
        `segmentation fault (core dumped)` 

## location.
https://github.com/huggingface/transformers/blob/v2.8.0/setup.py#L113



## configurations
- Platform:
- Torch version: torch==1.3.1
- Transformer version; transformers==2.8.0
- Python version: 3.7.3
- Using GPU in the script?: No.

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