Update version number based on build automatically

Right now, each build requires me to set the version for lovebrew manually (and I've already messed this up several times). Ideally we only build on release, but run tests and whatnot on push. That way each commit is still verified, but the build process knows which tag to set the version for.

https://github.com/MisterDA/love-release also reads information in the conf.lua file, which would be useful to set based on the tag.