Bump flake8 from 3.8.3 to 3.8.4

Bumps [flake8](https://gitlab.com/pycqa/flake8) from 3.8.3 to 3.8.4.
- [Release notes](https://gitlab.com/pycqa/flake8/tags)
- [Commits](https://gitlab.com/pycqa/flake8/compare/3.8.3...3.8.4)

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

Author: dependabot[bot]

poetry.lock

@@ -15,7 +15,7 @@ requests = "2.*"
 [tool.poetry.dev-dependencies]
 coveralls = "^2.1.2"
 isort = "^5.5"
-flake8 = "^3.8.3"
+flake8 = "^3.8.4"
 black = { version = "==20.8b1", allow-prereleases = true }
 
 [build-system]