No git tag for latest releases

According to https://rubygems.org/gems/multi_json versions `1.16.0` and `1.17.0` are out, but on https://github.com/intridea/multi_json/tags I don't see them.

The reason why I'm asking is because I maintain the Arch Linux package for this gem and we build from git tags and not from rubygems, so we can't ship the latest version if there is no git tag for it.

Best regards
Segaja