countries() returns no results for 'America/Cordoba'

[maxhawkins]

While testing different time zones, I found an issue with the "America/Cordoba" zone and the countries() method.

moment.tz.guess() returned "America/Cordoba", which is in Argentina. However:

moment.tz.zone("America/Cordoba").countries() === []

[ichernev]

		test.deepEqual(tz.zone('America/Argentina/Cordoba').countries(), ["AR"]);
		test.deepEqual(tz.zone('America/Cordoba').countries(), []);

This is because America/Cordoba is deprecated in favor of America/Argentina/Cordoba and some browsers (via Intl) return the deprecated timezone.

Close in favor of #873