Bump nltk from 3.4.5 to 3.6.6 in /unsupported/attack-predictor/1.0.0

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] <[email protected]>

Author: dependabot[bot]

unsupported/attack-predictor/1.0.0/requirements.txt

@@ -1,7 +1,7 @@
 joblib==0.14.1
 numpy==1.17.4
 stix2==1.2.1
-nltk==3.4.5
+nltk==3.6.6
 colorama
 pandas==0.25.3
 #scikit-learn==0.22.2.post1