Bump pygments from 2.7.4 to 2.15.0 (#66)

Bumps [pygments](https://github.com/pygments/pygments) from 2.7.4 to 2.15.0.
- [Release notes](https://github.com/pygments/pygments/releases)
- [Changelog](https://github.com/pygments/pygments/blob/master/CHANGES)
- [Commits](pygments/pygments@2.7.4...2.15.0)

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

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Author: dependabot[bot]

docs_requirements.txt

@@ -1,6 +1,6 @@
 Jinja2==2.11.3
 PyYAML==5.4
-Pygments==2.7.4
+Pygments==2.15.0
 Sphinx==1.2b1
 cov-core==1.7
 coverage==3.6