chore(deps): bump aiohttp from 2.3.7 to 3.7.4

Bumps [aiohttp](https://github.com/aio-libs/aiohttp) from 2.3.7 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@v2.3.7...v3.7.4)

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

Author: dependabot[bot]

requirements.txt

@@ -1,4 +1,4 @@
-aiohttp==2.3.7
+aiohttp==3.7.4
 async-timeout==2.0.0
 asyncio==3.4.3
 chardet==3.0.4

setup.py

@@ -5,7 +5,7 @@
 here = os.path.abspath(os.path.dirname(__file__))
 
 requires = [
-        'aiohttp==2.3.7',
+        'aiohttp==3.7.4',
         'asyncio==3.4.3',
         'graypy==0.2.14',
         'pillow==5.2.0',