Bump pygments from 2.5.2 to 2.7.4 in /docker

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] <[email protected]>

Author: dependabot[bot]

docker/requirements.txt

@@ -4,5 +4,5 @@ hacking==2.0.0
 htmlmin==0.1.12
 Jinja2==2.11.1
 Markdown==3.2.1
-Pygments==2.5.2
+Pygments==2.7.4
 regex==2020.2.20