Bump flake8-isort from 3.0.1 to 4.0.0

Bumps [flake8-isort](https://github.com/gforcada/flake8-isort) from 3.0.1 to 4.0.0.
- [Release notes](https://github.com/gforcada/flake8-isort/releases)
- [Changelog](https://github.com/gforcada/flake8-isort/blob/master/CHANGES.rst)
- [Commits](gforcada/flake8-isort@3.0.1...4.0.0)

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

requirements-lint.txt

@@ -9,7 +9,7 @@ flake8-django==1.1.1
 flake8-docstrings==1.5.0
 flake8-eradicate==0.4.0
 flake8-executable==2.0.3
-flake8-isort==3.0.1
+flake8-isort==4.0.0
 flake8-logging-format==0.6.0
 flake8-mutable==1.2.0
 flake8-no-u-prefixed-strings==0.2