Bump pycodestyle from 2.5.0 to 2.6.0

Bumps [pycodestyle](https://github.com/PyCQA/pycodestyle) from 2.5.0 to 2.6.0.
- [Release notes](https://github.com/PyCQA/pycodestyle/releases)
- [Changelog](https://github.com/PyCQA/pycodestyle/blob/master/CHANGES.txt)
- [Commits](https://github.com/PyCQA/pycodestyle/compare/2.5.0...2.6.0)

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

requirements-dev.txt

@@ -1,7 +1,7 @@
 coverage
 mock
 nose
-pycodestyle==2.5.0
+pycodestyle==2.6.0
 pyflakes==2.2.0
 readme_renderer[md]==26.0
 requests_mock