add nltk requirement to latest version

pyproject.toml

@@ -23,6 +23,7 @@ dependencies = [
     "gradio[oauth]>=5.4.0,<6.0.0",
     "gradio-huggingfacehub-search>=0.0.12,<1.0.0",
     "model2vec>=0.2.4,<1.0.0",
+    "nltk>=3.9.1,<4.0.0",
     "pydantic>=2.10.5,<3.0.0",
     "sentence-transformers>=3.2.0,<4.0.0",
     "transformers>=4.44.2,<5.0.0",