Surprisingly Travis fails on MacOS: https://travis-ci.com/aio-libs/aiohttp/builds/98188999?utm_medium=notification&utm_source=email

Looks like it is the result of my #3548 PR.
I have no Mac available, the investigation can be slow.
If somebody can run tests locally on Mac and debug what is wrong -- it would be awesome and save my personal time a lot.