This also adjusts Bundler to be explicitly fixed at either 1.17.2 or the Ruby/Rubygems-bundled version, whichever is newer -- this is slightly older than what we've already pushed (1.17.3), but nothing in the changelog appears to be relevant, so this seems fine: https://github.com/bundler/bundler/compare/v1.17.2...v1.17.3#diff-4ac32a78649ca5bdd8e0ba38b7006a1e
For Ruby 2.6, this means we no longer do anything to the bundled Rubygems (or Bundler), and simply provide whatever comes with the Ruby release as-is, and it is now up to users to explicitly update if they need a newer version than is provided here.
