Update for python 3.7

[phdye]

Just a few minor changes for 3.7

[emmatyping]

Thank you for working on this. I havent been focusing on this repo for a while, but I recently have been trying to find the best way to handle distribution of this package, and what the compatibility should look like, I think I will want to backport compatibility with future Python versions, so I will likely accept this, or something like this in the next few days.

[XVilka]

Note, that many popular distributions already provide python 3.7+ versions.