Plugin defines global `M`

[AThePeanut4]

In git.lua, M is (I assume) accidentally defined as global rather than local: https://github.com/chrishrb/gx.nvim/blob/c7e6a0ace694a098a5248d92a866c290bd2da1cc/lua/gx/git.lua#L1

This doesn't really cause anything bad to happen, it is mostly just annoying because luals picks the global up and allows it to be used everywhere. Also since there's no type annotations it also allows you to do anything with it without throwing errors.

It is literally just a one word fix so it feels silly for me to make a entire PR, but I'm happy to do that if needed.