build(deps): pinned nltk version to address build failure

[kirupang-code]

Build failed due to nltk version update, so I downgraded the version to temporarily fix the issue.
Here's the error that was generated:

E       LookupError:
--
4975 | E       **********************************************************************
4976 | E         Resource punkt_tab not found.
4977 | E         Please use the NLTK Downloader to obtain the resource:
4978 | E
4979 | E         >>> import nltk
4980 | E         >>> nltk.download('punkt_tab')
4981 | E
4982 | E         For more information see: https://www.nltk.org/data.html
4983 | E
4984 | E         Attempted to load tokenizers/punkt_tab/english/
4985 | E
4986 | E         Searched in:
4987 | E           - '/root/nltk_data'
4988 | E           - '/codebuild/output/src862412924/src/venv/nltk_data'
4989 | E           - '/codebuild/output/src862412924/src/venv/share/nltk_data'
4990 | E           - '/codebuild/output/src862412924/src/venv/lib/nltk_data'
4991 | E           - '/usr/share/nltk_data'
4992 | E           - '/usr/local/share/nltk_data'
4993 | E           - '/usr/lib/nltk_data'
4994 | E           - '/usr/local/lib/nltk_data'
4995 | E       **********************************************************************
4996 |  
4997 | venv/lib/python3.10/site-packages/nltk/data.py:582: LookupError

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