feat(nvim): specifically clone Neovim v0.5.0 on Debian
feat(nvim): specifically clone Neovim v0.5.0 on Debian

For stability, now that the release is out, we can stop tracking `HEAD`.
I don't necessarily want to run "NVIM v0.6.0-dev+42-geece0735f" or
similar on a work machine.

This matches what I am doing on macOS/Arch (I'm not building from
source, but I am using the release).

wincent/wincent,wincent/wincent,wincent/wincent,wincent/wincent,wincent/wincent,wincent/wincent,wincent/wincent,wincent/wincent