Bump flake8 from 3.8.2 to 3.8.3

Bumps [flake8](https://gitlab.com/pycqa/flake8) from 3.8.2 to 3.8.3.
- [Release notes](https://gitlab.com/pycqa/flake8/tags)
- [Commits](https://gitlab.com/pycqa/flake8/compare/3.8.2...3.8.3)

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

test_reqs.txt

@@ -1,7 +1,7 @@
 django-treebeard==4.3.1
 Markdown>=2.6.11,<3
 coverage==5.1
-flake8==3.8.2
+flake8==3.8.3
 django-jenkins==0.110.0
 pep8==1.7.1
 pyflakes==2.2.0