fix nltk punkt

Author: Richard Kuo (Onyx)

backend/Dockerfile

@@ -85,7 +85,7 @@ Tokenizer.from_pretrained('nomic-ai/nomic-embed-text-v1')"
 # Pre-downloading NLTK for setups with limited egress
 RUN python -c "import nltk; \
 nltk.download('stopwords', quiet=True); \
-nltk.download('punkt', quiet=True);"
+nltk.download('punkt_tab', quiet=True);"
 # nltk.download('wordnet', quiet=True); introduce this back if lemmatization is needed
 
 # Set up application files