Bump pygments from 2.6.1 to 2.15.0

Bumps [pygments](https://github.com/pygments/pygments) from 2.6.1 to 2.15.0.
- [Release notes](https://github.com/pygments/pygments/releases)
- [Changelog](https://github.com/pygments/pygments/blob/master/CHANGES)
- [Commits](pygments/pygments@2.6.1...2.15.0)

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

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

Author: dependabot[bot]

requirements.txt

@@ -63,7 +63,7 @@ pycosat==0.6.3
 pycparser==2.20
 pyecore==0.11.7
 pygeppetto==0.8.1
-Pygments==2.6.1
+Pygments==2.15.0
 PyJWT==1.7.1
 PyLEMS==0.4.9.3
 pyNeuroML>=0.7.1