Bump aiohttp from 3.1.3 to 3.7.4

Bumps [aiohttp](https://github.com/aio-libs/aiohttp) from 3.1.3 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@v3.1.3...v3.7.4)

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

Author: dependabot[bot]

requirements.txt

@@ -3,4 +3,4 @@ Markdown
 html2text==2014.12.29
 lxml==3.5
 parse==1.8.2
-aiohttp==3.1.3
+aiohttp==3.7.4

setup.py

@@ -11,7 +11,7 @@ def read(f):
 
 install_requires = [
     'sdiff @ git+https://github.com/KeepSafe/html-structure-diff.git#egg=sdiff',
-    'aiohttp >=3, <3.4',
+    'aiohttp >=3, <3.8',
     'Markdown',
     'parse >=1, <2',
     'beautifulsoup4 >=4, <5',