"fatal: not a git repository" when building from source tarball/zip

[polprog]

The build dockerfile attempts to do git submodule update --init --recursive, but this causes an error when ran from a tree that was unpacked from the release zip or tar.gz file. This prevents compiling from the source tarball.

Step 10/10 : RUN git submodule update --init --recursive
 ---> Running in 0fba892d9091
fatal: not a git repository (or any of the parent directories): .git
The command '/bin/sh -c git submodule update --init --recursive' returned a non-zero code: 128
Unable to find image 'uvk5:latest' locally

As far as I can tell the repo contains no submodules, so this command is not necesary

(of course the solution is to git clone the repo instead, but building from the source tarball is nice)