Bump pygments from 2.6.1 to 2.7.1

Bumps [pygments](https://github.com/pygments/pygments) from 2.6.1 to 2.7.1.
- [Release notes](https://github.com/pygments/pygments/releases)
- [Changelog](https://github.com/pygments/pygments/blob/master/CHANGES)
- [Commits](https://github.com/pygments/pygments/compare/2.6.1...2.7.1)

sphinx-doc/requirements_sphinx.txt

@@ -35,7 +35,7 @@ pathspec==0.8.0
 pluggy==0.13.1
 py==1.8.1
 pyarrow==1.0.1
-Pygments==2.6.1
+Pygments==2.7.1
 pyparsing==2.4.6
 pytest==5.3.5
 pytest-lazy-fixture==0.6.3