Fix get_period_id() with dayPeriodRule across 0:00

[jun66j5]

Fix for #870.

[codecov]

Codecov Report

Merging #871 (17d1af9) into master (3ae5402) will decrease coverage by 0.01%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master     #871      +/-   ##
==========================================
- Coverage   91.34%   91.32%   -0.02%     
==========================================
  Files          23       23              
  Lines        4192     4198       +6     
==========================================
+ Hits         3829     3834       +5     
- Misses        363      364       +1     

Impacted Files	Coverage Δ
babel/dates.py	92.47% <100.00%> (-0.08%)	⬇️

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[akx]

Looks great, thank you! I would have added a comment noting that the first if statement takes care of rules that straddle days, but it's evident from the commit message. 😄