Bump pygments from 2.8.0 to 2.15.0

Bumps [pygments](https://github.com/pygments/pygments) from 2.8.0 to 2.15.0.
- [Release notes](https://github.com/pygments/pygments/releases)
- [Changelog](https://github.com/pygments/pygments/blob/master/CHANGES)
- [Commits](pygments/pygments@2.8.0...2.15.0)

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

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

requirements.txt

@@ -14,7 +14,7 @@ mkdocs-material==7.0.3
 mkdocs-material-extensions==1.0.1
 nltk==3.6.5
 packaging==20.9
-Pygments==2.8.0
+Pygments==2.15.0
 pymdown-extensions==8.1.1
 pyparsing==2.4.7
 python-dateutil==2.8.1