Import error due to rouge library

[Oguzhan Gencoglu]

from string2string.metrics import sacreBLEU

raises the error:

File ~/my_dir/lib/python3.9/site-packages/string2string/metrics/rouge.py:8
      1 """
      2     This module contains a wrapper class for the ROUGE metric.
      3 
      4     ROUGE (Recall-Oriented Understudy for Gisting Evaluation) is a set of metrics for evaluating the quality of summaries in machine translation, text summarization, and other natural language generation tasks.
      5 """
      7 from typing import Union, List, Dict
----> 8 from rouge_score import rouge_scorer
      9 from rouge_score.scoring import BootstrapAggregator
     10 from string2string.misc.default_tokenizer import Tokenizer

ModuleNotFoundError: No module named 'rouge_score'

Are the requirements up-to-date?