DeprecationWarnings with Python 3.8: "@coroutine" decorator

[hroncok]

=============================== warnings summary ===============================
tests/unit/test_cors_config.py:33
  .../tests/unit/test_cors_config.py:33: DeprecationWarning: "@coroutine" decorator is deprecated since Python 3.8, use "async def" instead
    def get(self):

tests/integration/test_main.py::test_dummy_setup[pyloop]
  /usr/lib64/python3.8/site-packages/aiohttp/web_server.py:53: DeprecationWarning: The loop argument is deprecated since Python 3.8, and scheduled for removal in Python 3.10.
    await asyncio.gather(*coros, loop=self._loop)

-- Docs: https://docs.pytest.org/en/latest/warnings.html
==================== 93 passed, 2 warnings in 2.61 seconds =====================

With current default tests config:

============================= test session starts ==============================
platform linux -- Python 3.8.0, pytest-5.2.2, py-1.8.0, pluggy-0.13.0
cachedir: .tox/py38/.pytest_cache
rootdir: /...aiohttp-cors, inifile: pytest.ini
plugins: cov-2.8.1, pylint-0.14.1, aiohttp-0.3.0
collected 91 items / 1 errors / 90 selected

==================================== ERRORS ====================================
_______________ ERROR collecting tests/unit/test_cors_config.py ________________
tests/unit/test_cors_config.py:30: in <module>
    class _View(web.View, CorsViewMixin):
tests/unit/test_cors_config.py:33: in _View
    def get(self):
/usr/lib64/python3.8/asyncio/coroutines.py:111: in coroutine
    warnings.warn('"@coroutine" decorator is deprecated since Python 3.8, use "async def" instead',
E   DeprecationWarning: "@coroutine" decorator is deprecated since Python 3.8, use "async def" instead
!!!!!!!!!!!!!!!!!!! Interrupted: 1 errors during collection !!!!!!!!!!!!!!!!!!!!
=============================== 1 error in 0.27s ===============================