dataset_converters error

[htaoruan]

python tools/dataset_converters/textrecog/rctw_converter.py ./data/rctw17 --val-ratio 0.2
File "anaconda3/envs/openmmocr/lib/python3.8/site-packages/mmengine/fileio/io.py", line 908, in dump raise TypeError(f'Unsupported format: {file_format}')
TypeError: Unsupported format:

[gaotongxiao]

Please fix it referring to https://github.com/open-mmlab/mmocr/pull/1859/files