Missing rss dependency on build

[AlexandreRio]

After building transmission-rss following the instructions from the README, the executable raises the following error:

<internal:/usr/lib/ruby/site_ruby/3.0.0/rubygems/core_ext/kernel_require.rb>:85:in `require': cannot load such file -- rss (LoadError)
        from <internal:/usr/lib/ruby/site_ruby/3.0.0/rubygems/core_ext/kernel_require.rb>:85:in `require'
        from /home/orb/dev/transmission-rss/lib/transmission-rss/aggregator.rb:3:in `<top (required)>'
        from <internal:/usr/lib/ruby/site_ruby/3.0.0/rubygems/core_ext/kernel_require.rb>:85:in `require'
        from <internal:/usr/lib/ruby/site_ruby/3.0.0/rubygems/core_ext/kernel_require.rb>:85:in `require'
        from /home/orb/dev/transmission-rss/lib/transmission-rss.rb:11:in `block in <top (required)>'
        from /home/orb/dev/transmission-rss/lib/transmission-rss.rb:10:in `each'
        from /home/orb/dev/transmission-rss/lib/transmission-rss.rb:10:in `<top (required)>'
        from <internal:/usr/lib/ruby/site_ruby/3.0.0/rubygems/core_ext/kernel_require.rb>:85:in `require'
        from <internal:/usr/lib/ruby/site_ruby/3.0.0/rubygems/core_ext/kernel_require.rb>:85:in `require'
        from ./bin/transmission-rss:7:in `<main>'

Manually installing rss using gem install rss fixes the issue.

• ruby -v

ruby 3.0.1p64 (2021-04-05 revision 0fb782ee38) [x86_64-linux]

• transmission-rss -v

1.3.0.pre