Upstream support for Ruby 2.0 ended at the beginning of 2016, therefore we'd like to remove ruby20 soon. Your package depends on ruby:2.0, please use a recent ruby implementation and get this version stable, if the ruby:2.0 version had stable keywords.
Thanks, fixed in git and targeted for stabilisation: https://gitweb.gentoo.org/repo/gentoo.git/commit/?id=4403c3564ef747e8207426c8d8fc7951abe72a58
Newer version stabilised and all older versions depending on ruby:2.0 are removed.