Update Ruby to >= 2.3.0

[bradleyknaysi]

The Bundler gem (which is very important for installations) has lost support for any Ruby version less than 2.3.0

• Try to slowly update to 2.3.0 or 2.4.4 or 2.5.3

• Update gems one by one or use commands like --conservative or --strict or --patch to minimize errors

[brian-yu]

👍 Agree that this should be a priority. We should try to update to 2.5 or 2.6. We can then try to update gems using bundle update --all --conservative.