[REQ][Ruby] Include the latest Ruby versions in the Travis CI build matrix

[szTheory]

Is your feature request related to a problem? Please describe.

No

Describe the solution you'd like

Include the latest Ruby versions in the Travis CI build (2.6, 2.7, 3.0)

Describe alternatives you've considered

Could leave it as is, but why have an out of date build matrix.

Additional context

It's been a few years since the initial Travis CI configuration for the Ruby module was added, so I assume the new Ruby versions were just not added because the maintainers are busy and nobody noticed such a minor detail.