Bump codecov from 2.1.7 to 2.1.8 in /src/requirements (#593)

Bumps [codecov](https://github.com/codecov/codecov-python) from 2.1.7 to 2.1.8.
- [Release notes](https://github.com/codecov/codecov-python/releases)
- [Changelog](https://github.com/codecov/codecov-python/blob/master/CHANGELOG.md)
- [Commits](https://github.com/codecov/codecov-python/compare/v2.1.7...2.1.8)

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

Co-authored-by: dependabot-preview[bot] <27856297+dependabot-preview[bot]@users.noreply.github.com>

src/requirements/dev.txt

@@ -3,7 +3,7 @@
 django-debug-toolbar==2.2
 factory_boy==2.12.0
 coverage==5.2
-codecov==2.1.7
+codecov==2.1.8
 black==19.10b0
 pre-commit==2.6.0
 isort==5.1.1