Deprecation warning in web_response.py with Python 3.7

[dmajda]

Long story short

When warnings are enabled, a warning like this is printed on importing aiohttp.web with Python 3.7:

/Users/dmajda/tmp/warnings/aiohttp/.venv/lib/python3.7/site-packages/aiohttp/web_response.py:33: DeprecationWarning: Using or importing the ABCs from 'collections' instead of from 'collections.abc' is deprecated, and in 3.8 it will stop working
  BaseClass = collections.MutableMapping

This pullutes the output of our test suite (for which we have warnings enabled).

Expected behaviour

No warning gets printed when importing aiohttp.web.

Actual behaviour

A warning gets printed when importing aiohttp.web.

Steps to reproduce

$ python3 --version
Python 3.7.0
$ python3 -m venv .venv
[...]
$ . .venv/bin/activate
$ pip3 install aiohttp
[...]
$ python3 -Wall -c 'import aiohttp.web'
/Users/dmajda/tmp/warnings/aiohttp/.venv/lib/python3.7/site-packages/aiohttp/web_response.py:33: DeprecationWarning: Using or importing the ABCs from 'collections' instead of from 'collections.abc' is deprecated, and in 3.8 it will stop working
  BaseClass = collections.MutableMapping

Your environment

aiohttp version: 3.5.1
Python version: 3.7.0
OS: macOS Mojave

[aio-libs-bot]

GitMate.io thinks the contributor most likely able to help you is @asvetlov.

Possibly related issues are #3273 (Deprecation warnings in 3.8), #537 (Drop python 3.3 support), #1839 (aiohttp webserver with python 3.7 broken), #676 (Python 3.4.0 support), and #3111 (Publish OS-specific binary wheels for Python 3.7 @ PYPI).

[webknjaz]

@dmajda feel free to send a PR :)

[dmajda]

Looks like @asvetlov was faster :-) Thanks for a quick fix and a fantastic library!

[lock]

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