Bump yapf from 0.30.0 to 0.31.0

Bumps [yapf](https://github.com/google/yapf) from 0.30.0 to 0.31.0.
- [Release notes](https://github.com/google/yapf/releases)
- [Changelog](https://github.com/google/yapf/blob/main/CHANGELOG)
- [Commits](google/yapf@v0.30.0...v0.31.0)

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

requirements.txt

@@ -3,4 +3,4 @@ click>=7.1.2
 consolekit>=0.3.0
 domdf-python-tools>=0.10.0
 isort<=5.6.4,>=5.5.2
-yapf==0.30.0
+yapf==0.31.0