Bump aiohttp in /libraries/botbuilder-integration-aiohttp

Bumps [aiohttp](https://github.com/aio-libs/aiohttp) from 3.6.2 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@v3.6.2...v3.7.4)

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

Author: dependabot[bot]

libraries/botbuilder-integration-aiohttp/requirements.txt

@@ -1,4 +1,4 @@
 msrest==0.6.10
 botframework-connector==4.12.0
 botbuilder-schema==4.12.0
-aiohttp==3.6.2
+aiohttp==3.7.4