python3.7 support

[sobolevn]

Hi, I am considering adding this tool as a plugin for my own linter: https://github.com/wemake-services/wemake-python-styleguide

But, I am missing python3.7 official support.
Are there any known problems?

I would be happy to work on this issue if you don't mind.

[bcaller]

There are no problems with python 3.7. I have added it as a test environment in #193.
Python 3.8 probably won't work immediately, but you can run pyt in a python 3.6 or 3.7 environment over code targeting 3.8.