Update deprecated CircleCI images

[getaaron]

Checklist

• I've run bundle exec rspec from the root directory to see all new and existing tests pass
• I've followed the fastlane code style and run bundle exec rubocop -a to ensure the code style is valid
• I see several green ci/circleci builds in the "All checks have passed" section of my PR (connect CircleCI to GitHub if not)
• I've read the Contribution Guidelines
• I've updated the documentation if necessary.

Motivation and Context

As part of CircleCI's Legacy Convenience Image Deprecation, we need to change the image namespace.

The new images should be "faster, more efficient, and most importantly, more reliable".

Description

Update CircleCI yml to point to new images.

Testing Steps

Observe all green builds on GitHub (hopefully)

[crazymanish]

💯