Drop support for Ruby 2.2, 2.3. (#1318)
Drop support for Ruby 2.2, 2.3. (#1318)

Continuing to have support for Ruby 2.2 and 2.3 are stopping us from
keeping up with security updates, even though they're technically still
supported by Rails.

In addition, 2.3 recently become EOL:
https://www.ruby-lang.org/en/news/2019/03/31/support-of-ruby-2-3-has-ended/
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