Add Offer class to Activity Vocabulary API

[moreal]

It resolves a part of #65. It adds Offer class to Activity Vocabulary API.

[dahlia]

You should update snapshots for snapshot tests. It can be updated by running deno task test -- --update.

[moreal]

@dahlia Thank you! I updated the snapshots and I'll mark as ready-for-review after the checks passed.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 81.55%. Comparing base (fd936ae) to head (a143a73).
Report is 3 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main      #76   +/-   ##
=======================================
  Coverage   81.55%   81.55%           
=======================================
  Files          39       39           
  Lines        5450     5450           
  Branches      628      628           
=======================================
  Hits         4445     4445           
  Misses        995      995           
  Partials       10       10           

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[moreal]

The publish-docs check is failing. It may have an error when using nwtgck/actions-netlify@v3.0 action 🤔 (I cannot see logs). Because #68 is merged though the task was failed in the PR too, I mark this pull request as ready-for-review.

[dahlia]

The publish-docs check is failing. It may have an error when using nwtgck/actions-netlify@v3.0 action 🤔 (I cannot see logs). Because #68 is merged though the task was failed in the PR too, I mark this pull request as ready-for-review.

That's my fault; I have to fix the CI. Never mind!