Bump flake8 from 3.7.8 to 3.7.9

Bumps [flake8](https://gitlab.com/pycqa/flake8) from 3.7.8 to 3.7.9.
- [Release notes](https://gitlab.com/pycqa/flake8/tags)
- [Commits](https://gitlab.com/pycqa/flake8/compare/3.7.8...3.7.9)

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

Author: dependabot-preview[bot]

setup.py

@@ -4,7 +4,7 @@
 EXTRAS_REQUIRE = {
     "yaml": ["PyYAML>=3.10"],
     "validation": ["prance[osv]>=0.11"],
-    "lint": ["flake8==3.7.8", "flake8-bugbear==19.8.0", "pre-commit~=1.18"],
+    "lint": ["flake8==3.7.9", "flake8-bugbear==19.8.0", "pre-commit~=1.18"],
     "docs": [
         "marshmallow>=2.19.2",
         "pyyaml==5.1.2",