Bump pygments from 2.2.0 to 2.6.1

Bumps [pygments](https://github.com/pygments/pygments) from 2.2.0 to 2.6.1.
- [Release notes](https://github.com/pygments/pygments/releases)
- [Changelog](https://github.com/pygments/pygments/blob/master/CHANGES)
- [Commits](pygments/pygments@2.2.0...2.6.1)

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

requirements_test.txt

@@ -9,4 +9,4 @@ pytest-cov==2.8.1
 pytest-sugar==0.9.2
 pytest-timeout==1.3.4
 restructuredtext-lint==1.0.1
-pygments==2.2.0
+pygments==2.6.1