fix: parsing compound cron expression fields

[reugn]

No description provided.

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 73.40426% with 25 lines in your changes are missing coverage. Please review.

Project coverage is 87.89%. Comparing base (8a940a4) to head (b3071f7).

Files	Patch %	Lines
quartz/cron.go	64.51%	14 Missing and 8 partials ⚠️
quartz/util.go	90.62%	2 Missing and 1 partial ⚠️

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Additional details and impacted files

@@            Coverage Diff             @@
##           master     #115      +/-   ##
==========================================
- Coverage   89.67%   87.89%   -1.78%     
==========================================
  Files          19       19              
  Lines         920      950      +30     
==========================================
+ Hits          825      835      +10     
- Misses         67       77      +10     
- Partials       28       38      +10     

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