This is an unfortunate consequence of depending on termbox, which uses Python as part of its build (waf), which unfortunately doesn't work in Python 3.7. On Arch, you need to alias python to python2 for the build to work. I'll comment on the AUR package.

As an aside, my current 0.6.0 feature is moving completely towards termion (a Rust-based, lower-level terminal lib) that'll resolve that!

AUR package is fixed; feel free to give it another shot. :)