Bump isort from 5.5.4 to 5.6.4 (#226)

Bumps [isort](https://github.com/pycqa/isort) from 5.5.4 to 5.6.4.
- [Release notes](https://github.com/pycqa/isort/releases)
- [Changelog](https://github.com/PyCQA/isort/blob/develop/CHANGELOG.md)
- [Commits](PyCQA/isort@5.5.4...5.6.4)

Signed-off-by: dependabot[bot] <[email protected]>

Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>

Author: dependabot[bot]

requirements.txt

@@ -22,7 +22,7 @@ coverage==5.3
 flake8==3.8.4
 flake8-bugbear==20.1.4
 flake8-pie==0.6.1
-isort==5.5.4
+isort==5.6.4
 mypy==0.790
 pproxy==2.3.7
 pytest==6.1.2