Bump nltk from 3.6.4 to 3.6.6 (facebookresearch#4301)

Bumps [nltk](https://github.com/nltk/nltk) from 3.6.4 to 3.6.6.
- [Release notes](https://github.com/nltk/nltk/releases)
- [Changelog](https://github.com/nltk/nltk/blob/develop/ChangeLog)
- [Commits](nltk/nltk@3.6.4...3.6.6)

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

Signed-off-by: dependabot[bot] <[email protected]>

Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>

requirements.txt

@@ -16,7 +16,7 @@ hydra-core~=1.1.0
 ipython==7.19.0
 torch>=1.4.0
 joblib==0.14.1
-nltk==3.6.4
+nltk==3.6.6
 omegaconf~=2.1.1
 pandas==1.1.1
 pytest_regressions==2.1.1