Added Hong Kong (zh_hk) locale

[sunnz]

Pull Request Checklist

• 🧪 Added tests for changed code.
• 🛠️ All tests pass when run locally (run tox or make test to find out!).
• 📚 Updated documentation for changed code.
• ⏩ Code is up-to-date with the master branch.

Description of Changes

Added Hong Kong (zh_hk) locale with its unit test

[codecov-io]

Codecov Report

Merging #742 into master will not change coverage.
The diff coverage is 100%.

@@          Coverage Diff          @@
##           master   #742   +/-   ##
=====================================
  Coverage     100%   100%           
=====================================
  Files           9      9           
  Lines        1678   1687    +9     
  Branches      283    283           
=====================================
+ Hits         1678   1687    +9

Impacted Files	Coverage Δ
arrow/locales.py	100% <100%> (ø)	⬆️

---

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 70fb905...a75f3bb. Read the comment docs.

[jadchaar]

LGTM