Sangjun Park

`rouge-score` library erase all non alphanumeric characters. So cannot be used to calculate Korean characters.

Error ocuured on pretraining with transformers>=4.12 like below ``` /nas/home/psj8252/personal/transformers-bart-training/venv/lib/python3.7/site-packages/tensorflow/python/distribute/one_device_strategy.py:188 run [24/426] return super(OneDeviceStrategy, self).run(fn, args, kwargs, options) /nas/home/psj8252/personal/transformers-bart-training/venv/lib/python3.7/site-packages/tensorflow/python/distribute/distribute_lib.py:1259 run return self._extended.call_for_each_replica(fn, args=args, kwargs=kwargs) /nas/home/psj8252/personal/transformers-bart-training/venv/lib/python3.7/site-packages/tensorflow/python/distribute/distribute_lib.py:2730 call_for_each_replica return self._call_for_each_replica(fn, args, kwargs)...