Bump nltk from 3.4.5 to 3.9

Bumps [nltk](https://github.com/nltk/nltk) from 3.4.5 to 3.9.
- [Changelog](https://github.com/nltk/nltk/blob/develop/ChangeLog)
- [Commits](nltk/nltk@3.4.5...3.9)

---
updated-dependencies:
- dependency-name: nltk
  dependency-type: direct:production
...

Signed-off-by: dependabot[bot] <support@github.com>

setup.py

@@ -61,7 +61,7 @@ def get_version(rel_path):
         "pyjnius==1.2.1",
         "pymagnitude==0.1.143",
         "h5py==2.10.0",
-        "nltk==3.4.5",
+        "nltk==3.9",
         "pytest-mock",
         "mock",
         "pyserini==0.13.0",