MCprep is moving towards a new 5-stage development cycle (Stage 0 to 4),
where Stage 4 involves creating release candidates for testing and
feedback purposes. Release candiates use the format "#.#.#.#-rc-#" for
tags, to make them distinct from regular releases.

The addon updater should ignore these release candidates, as stability
is not guranteed.

Instead of checking for just rc, we also check for alpha and beta

Co-authored-by: Patrick W. Crawford <theduckcow@live.com>