fix: 0 is forbidden for day

[millotp]

According to the cron specification, the allowed values for the day segment must be between 1-31, but currently the cron * * 0 * * is allowed.

This PR aims at making IsValid("* * 0 * *") return false.

[codecov-commenter]

Codecov Report

Merging #32 (8aee396) into main (5a6b134) will not change coverage.
Report is 2 commits behind head on main.
The diff coverage is 100.00%.

❗ Your organization needs to install the Codecov GitHub app to enable full functionality.

@@           Coverage Diff           @@
##             main      #32   +/-   ##
=======================================
  Coverage   94.78%   94.78%           
=======================================
  Files           9        9           
  Lines         594      594           
=======================================
  Hits          563      563           
  Misses         16       16           
  Partials       15       15           

Files Changed	Coverage Δ
checker.go	100.00% <100.00%> (ø)
validator.go	100.00% <100.00%> (ø)

[adhocore]

thank you very much for your PR. i will check next day, is that okay?

[millotp]

Hey, no problem thanks for the response

[adhocore]

merged/released https://github.com/adhocore/gronx/releases/tag/v1.6.6 thanks