Bump aiohttp from 3.5.4 to 3.7.4

Bumps [aiohttp](https://github.com/aio-libs/aiohttp) from 3.5.4 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@v3.5.4...v3.7.4)

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

Author: dependabot[bot]

requirements.txt

@@ -5,6 +5,6 @@ pytest-mock==1.10.3
 pytest-mypy==0.4.1
 pytest-flakes==4.0.0
 # because of pip bug https://github.com/pypa/pip/issues/4780
-aiohttp==3.5.4
+aiohttp==3.7.4
 certifi==2019.3.9
 psutil==5.6.6; sys_platform == 'darwin'