snapcraft assign special meaning to version:git

A snapcraft.yaml with `version: git` has special meaning to snapcraft, supposedly that the version should be picked from the git ref of the repo clone where the snapcraft.yaml lives.

This results in failed snapcrafting when the directory is in fact not a git clone at all

Determining the version from the project repo (version: git).
fatal: Not a git repository (or any of the parent directories): .git

This behavior entirely undocumented outside the crappy error after building.