Bump isort from 5.8.0 to 5.9.1 (#261)

Bumps [isort](https://github.com/pycqa/isort) from 5.8.0 to 5.9.1.
- [Release notes](https://github.com/pycqa/isort/releases)
- [Changelog](https://github.com/PyCQA/isort/blob/main/CHANGELOG.md)
- [Commits](PyCQA/isort@5.8.0...5.9.1)

---
updated-dependencies:
- dependency-name: isort
  dependency-type: direct:development
  update-type: version-update:semver-minor
...

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

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

setup.py

@@ -31,7 +31,7 @@ def readme():
             "black==21.6b0",
             "docformatter==1.4",
             "flake8==3.9.2",
-            "isort==5.8.0",
+            "isort==5.9.1",
             "pytest==6.2.4",
             "pytest-cov==2.12.1",
             "pytype==2021.6.17",