Ruby 3 support

[taw]

Could you release a new version of the gem?

The most recent one is from 2018, and it depends on json 1.x, and that doesn't work on Ruby 3.

I see the gemspec was already fixed to not have dependency on json 1.x, so if you release what you have, it would fix Ruby 3 support.

[dreeves]

Thanks so much! On it.

Background: https://dev.to/taw/open-source-adventures-episode-37-fixing-beeminder-gem-to-work-with-ruby-3-d1c

[bsoule]

done!

[dreeves]

http://beeminder.com/changelog#4116