Bump aiohttp from 3.7.3 to 3.7.4 in /requirements (#562)

Bumps [aiohttp](https://github.com/aio-libs/aiohttp) from 3.7.3 to 3.7.4.
- [Release notes](https://github.com/aio-libs/aiohttp/releases)
- [Changelog](https://github.com/aio-libs/aiohttp/blob/master/CHANGES.rst)
- [Commits](aio-libs/aiohttp@v3.7.3...v3.7.4)

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

Co-authored-by: dependabot[bot] <49699333+dependabot[bot]@users.noreply.github.com>

requirements/ci.txt

@@ -3,6 +3,6 @@ docutils==0.16
 tox==3.23.0
 tox-travis==0.12
 pygments==2.7.3
-aiohttp==3.7.3
+aiohttp==3.7.4
 yarl==1.6.3
 multidict==5.1.0