The "0.5.0-1" rockspec on luarocks has a bug, resulting in it pulling
the current git master version, which is what we have effectively been
using.
Given that 0.5.0-1 is the latest release, is 6 years old, and that there
have been some bug fixes since then, we do actually want to be using the
git master version, but we also want to be using the correct rockspec
(particularly as alt-getopt has been replaced by argparse in the `moon`
binary).
