Update bin/readability to work with Ruby 3.x

[apainintheneck]

These changes should be backwards compatible with older Ruby versions according to the docs and testing it on Ruby 2.7 and 3.2.

Changes:

1. Use require_relative to avoid loading errors.
2. Use URI.parse(...).read instead of open(...).read
   • This seems to be backwards compatible with older Ruby versions. - Ex. https://www.rubydoc.info/stdlib/open-uri/2.3.1/OpenURI
   • The behavior should be identical to what we saw before.
   • open(...).read got deprecated in Ruby 3.0

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Do you think it's worth adding an integration test for this on CI?

Something like this would probably work to sanity check this. Probably would need to add more Rubies to CI though to make it a better check. Maybe not worth the effort.

bin/readability https://github.com/cantino/ruby-readability

[cantino]

Thanks @apainintheneck!