fix: "require 'set'" for models

[bednar]

Closes #84

Proposed Changes

The Ruby v3.0.1 requires explicit "import" of set.

Checklist

• CHANGELOG.md updated
• Rebased/mergeable
• rake test completes successfully
• Commit messages are in semantic format
• Sign CLA (if not already signed)

[codecov-commenter]

Codecov Report

Merging #86 (eaf11a8) into master (450e003) will not change coverage.
The diff coverage is n/a.

@@           Coverage Diff           @@
##           master      #86   +/-   ##
=======================================
  Coverage   98.98%   98.98%           
=======================================
  Files          16       16           
  Lines         785      785           
=======================================
  Hits          777      777           
  Misses          8        8           

---

Continue to review full report at Codecov.

Legend - Click here to learn more
Δ = absolute <relative> (impact), ø = not affected, ? = missing data
Powered by Codecov. Last update 450e003...eaf11a8. Read the comment docs.