improved parsing of timezone abbreviations

[jamesboi951]

Pull Request Checklist

Thank you for taking the time to improve Arrow! Before submitting your pull request, please check all appropriate boxes:

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

If you have any questions about your code changes or any of the points above, please submit your questions along with the pull request and we will try our best to help!

Description of Changes

Closes: #1065. improved parsing of timezone abbreviations.

[codecov]

Codecov Report

Merging #1103 (c16aba6) into master (5f9dfbe) will decrease coverage by 0.08%.
The diff coverage is 66.66%.

@@             Coverage Diff             @@
##            master    #1103      +/-   ##
===========================================
- Coverage   100.00%   99.91%   -0.09%     
===========================================
  Files           10       10              
  Lines         2325     2331       +6     
  Branches       449      450       +1     
===========================================
+ Hits          2325     2329       +4     
- Misses           0        1       +1     
- Partials         0        1       +1     

Impacted Files	Coverage Δ
arrow/arrow.py	99.64% <66.66%> (-0.36%)	⬇️

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