Bump flake8 from 3.8.4 to 3.9.2

Bumps [flake8](https://gitlab.com/pycqa/flake8) from 3.8.4 to 3.9.2.
- [Release notes](https://gitlab.com/pycqa/flake8/tags)
- [Commits](https://gitlab.com/pycqa/flake8/compare/3.8.4...3.9.2)

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

Author: dependabot-preview[bot]

setup.py

@@ -21,7 +21,7 @@ def run(self):
 
 
 tests_require = [
-    'flake8==3.8.4',
+    'flake8==3.9.2',
     'hypothesis==4.24.4',
 ]
 

test_reqs.txt

@@ -1,2 +1,2 @@
-flake8==3.8.4
+flake8==3.9.2
 hypothesis==4.24.4