[URGENT] fix: remove intl constraint

[dariof28]

The package cannot be installed anymore because of intl version conflict. This error is reported on pub.dev too -> https://pub.dev/packages/horizontal_calendar_widget/score

Because horizontal_calendar_widget depends on flutter_localizations any from sdk which depends on intl 0.17.0, intl 0.17.0 is required.
So, because horizontal_calendar_widget depends on intl ^0.16.1, version solving failed.

flutter_localizations already include intl dependency so is not necessary to add a direct dependency with version constraint

[codecov-commenter]

Codecov Report

Merging #19 (4f1ae53) into master (a53d83d) will decrease coverage by 0.03%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##           master      #19      +/-   ##
==========================================
- Coverage   98.42%   98.38%   -0.04%     
==========================================
  Files           3        3              
  Lines         127      124       -3     
==========================================
- Hits          125      122       -3     
  Misses          2        2              

Impacted Files	Coverage Δ
lib/date_helper.dart	100.00% <0.00%> (ø)

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