Bump flake8 from 3.7.9 to 3.8.1

Bumps [flake8](https://gitlab.com/pycqa/flake8) from 3.7.9 to 3.8.1.
- [Release notes](https://gitlab.com/pycqa/flake8/tags)
- [Commits](https://gitlab.com/pycqa/flake8/compare/3.7.9...3.8.1)

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

Author: dependabot-preview[bot]

poetry.lock

@@ -23,7 +23,7 @@ importlib_metadata = {version = "^1.6.0", python = "<3.8"}
 [tool.poetry.dev-dependencies]
 codecov = "^2.0.16"
 black = "^19.10b0"
-flake8 = "^3.7.9"
+flake8 = "^3.8.1"
 flake8-bandit = "^2.1.2"
 flake8-black = "^0.1.1"
 flake8-bugbear = "^20.1.4"