V1 backport ActiveAdmin v3 support and release new version

[difernandez]

Motivation / Background

This Pull Request has been created because in #477 we made some changes in order for this gem to be compatible with the recently released AA v3, but those changes are, as of now, only available in v2 (now in beta) of this gem. Even though we won't be supporting or backporting features to v1, we think it would be good to backport this particular changes to increase overall compatibility.

Detail

This Pull Request backports said changes in #477 to support v3 of ActiveAdmin in v1 of this gem. Also, in order, for tests to pass, needed to update to most recent ruby and also backport #476 to fix the webdriver issues, and remove EOL rubies from the CI.

Additional information

Checklist

Before submitting the PR make sure the following are checked:

• This Pull Request is related to one change. Changes that are unrelated should be opened in separate PRs.
• Commit message has a concise description of what changed and why.
• Tests are added or updated if you fix a bug or add a feature.
• Documentation has been added or updated if you add a feature or modify an existing one.
• CHANGELOG files are updated for the changed libraries if there is a behavior change or additional feature (under the "Unreleased" heading if this is not a version change).
• My changes don't introduce any linter rule violations.