Bump aiohttp from 3.7.4.post0 to 3.8.1

Bumps [aiohttp](https://github.com/aio-libs/aiohttp) from 3.7.4.post0 to 3.8.1.
- [Release notes](https://github.com/aio-libs/aiohttp/releases)
- [Changelog](https://github.com/aio-libs/aiohttp/blob/master/CHANGES.rst)
- [Commits](aio-libs/aiohttp@v3.7.4.post0...v3.8.1)

---
updated-dependencies:
- dependency-name: aiohttp
  dependency-type: direct:production
  update-type: version-update:semver-minor
...

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

Author: dependabot[bot]

requirements.txt

@@ -8,7 +8,7 @@ aiodns==3.0.0
     # via fdiff (setup.py)
 aiofiles==0.8.0
     # via fdiff (setup.py)
-aiohttp==3.7.4.post0
+aiohttp==3.8.1
     # via fdiff (setup.py)
 async-timeout==3.0.1
     # via aiohttp