Bump aiohttp from 3.7.2 to 3.7.3

Bumps [aiohttp](https://github.com/aio-libs/aiohttp) from 3.7.2 to 3.7.3.
- [Release notes](https://github.com/aio-libs/aiohttp/releases)
- [Changelog](https://github.com/aio-libs/aiohttp/blob/master/CHANGES.rst)
- [Commits](aio-libs/aiohttp@v3.7.2...v3.7.3)

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

requirements/ci.txt

@@ -3,6 +3,6 @@ docutils==0.16
 tox==3.20.1
 tox-travis==0.12
 pygments==2.7.2
-aiohttp==3.7.2
+aiohttp==3.7.3
 yarl==1.6.3
 multidict==5.0.2