Bump pygments from 2.5.2 to 2.7.4

Bumps [pygments](https://github.com/pygments/pygments) from 2.5.2 to 2.7.4.
- [Release notes](https://github.com/pygments/pygments/releases)
- [Changelog](https://github.com/pygments/pygments/blob/master/CHANGES)
- [Commits](pygments/pygments@2.5.2...2.7.4)

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

requirements-dev.txt

@@ -5,7 +5,7 @@
 Sphinx==1.8.5 ; python_version < '3.5'
 Sphinx==3.2.1 ; python_version >= '3.5'
 sphinxcontrib-httpdomain==1.7.0
-pygments==2.5.2
+pygments==2.7.4
 
 # Linting
 flake8==3.7.8