Bump nltk from 3.4.5 to 3.6.6

Bumps [nltk](https://github.com/nltk/nltk) from 3.4.5 to 3.6.6.
- [Release notes](https://github.com/nltk/nltk/releases)
- [Changelog](https://github.com/nltk/nltk/blob/develop/ChangeLog)
- [Commits](nltk/nltk@3.4.5...3.6.6)

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

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

Author: dependabot[bot]

requirements.txt

@@ -2,7 +2,7 @@ celery==4.2.1
 django==2.2.28
 django-environ==0.4.5
 h5py==2.9.0
-nltk==3.4.5
+nltk==3.6.6
 numpy==1.18.0
 psycopg2-binary==2.7.7
 scipy==1.2.0