Armenia is not supported #178

Summary

The ISO 3166 country code of Armenia is AM. Armenia is not included in the CountryExtended nor CountryExtendedExpanded enum. Please correct me if it is on purpose and Armenia is indeed an unsupported country.

Expected Behavior

The enums should include AM / ARMENIA as one of the possible values.

https://github.com/lob/lob-php/blob/main/lib/Model/CountryExtended.php
https://github.com/lob/lob-php/blob/main/lib/Model/CountryExtendedExpanded.php

Current Behavior

AM / ARMENIA is not a supported country.

Possible Solution

Add AM / ARMENIA as one of the supported countries.

Steps to Reproduce

1. \OpenAPI\Client\Model\CountryExtended::from('AM')
2. See exception: "AM" is not a valid backing value for enum OpenAPI\Client\Model\CountryExtended