Address deprecation warning in Unit Tests

[michael-lloyd-morris]

🤔 What's changed?

Fixing a deprecation warning in the unit tests.

> mocha 'src/**/*_spec.ts'



  ........(node:38244) [DEP0147] DeprecationWarning: In future versions of Node.js, fs.rmdir(path, { recursive: true }) will be removed. Use fs.rm(path, { recursive: true }) instead
(Use `node --trace-deprecation ...` to show where the warning was created)
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  326 passing (4s)

⚡️ What's your motivation?

Bugfix - well, a potential bug when the Node team finally follows up on the deprecation.

🏷️ What kind of change is this?

• 🐛 Bug fix (non-breaking change which fixes a defect)

📋 Checklist:

• I agree to respect and uphold the Cucumber Community Code of Conduct
• I've changed the behaviour of the code
  • I have added/updated tests to cover my changes.
• My change requires a change to the documentation.
  • I have updated the documentation accordingly.
• Users should know about my change
  • I have added an entry to the "Unreleased" section of the CHANGELOG, linking to this pull request.

[michael-lloyd-morris]

Apparently mz/fs doesn't have the new version of fs.rm in its implementation - that or it's incompatible with the old one the deprecation warns about. In any event, to resolve the deprecation I had to resort to the older Promise.then pattern.

[coveralls]

Coverage: 98.561% (+0.0006%) from 98.561% when pulling 3b94338 on michael-lloyd-morris:fixDeprecation into 627030d on cucumber:main.