Fixed. doesn't work on Ruby 3.0
Fixed. doesn't work on Ruby 3.0

`rss` gem is moved to bundled gem

c.f. https://www.ruby-lang.org/en/news/2020/12/25/ruby-3-0-0-released/

geminabox/geminabox,geminabox/geminabox,geminabox/geminabox,geminabox/geminabox