Use of Ruby Date.strptime(date_string, format) versus date_object.strftime(format)

[jrjamespdx]

Overview

Date format validation is currently not working as expected and definitely not working for ISO8601 validation. The issue seems to be that the lib/tableschema/types/date.rb cast_fmt method uses Date.strptime with flags from the iso8601 method, but Date.strptime does not support flags, but date_object.strftime does.

Links to docs:
https://ruby-doc.org/stdlib-2.5.3/libdoc/date/rdoc/Date.html#method-c-strptime
https://ruby-doc.org/stdlib-2.5.3/libdoc/date/rdoc/Date.html#method-i-strftime

I'll submit a PR for a change shortly.

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[roll]

Thanks @jrjamespdx !