Update Cirleci docker image

[mejiaj]

Summarize the issue in one sentence

CirlcleCI is showing a deprecated docker image warning.

Tell us more about how we can help

We should update this image in circleci/config.yml so builds can continue to work in the future.

Details

Let's update the image to use the new standard
https://circleci.com/developer/images/image/cimg/ruby

[nick-mon1]

This will be closed out when site is migrated.