getCode method for city instance return geoname instead of iso_3166_2

[raftalks]

The data does provides ids. iso_3166_2 but in the city class, both geonames and the code is the same value.

https://github.com/MenaraSolutions/geographer/blob/master/src/City.php#L25

[dusterio]

At the moment Geonames Id is the only public/third-party identification for cities. ISO doesn't issue city codes