Fix USA's state geojson for 'Country Map' visualization

[mistercrunch]

Turns out the ISO codes were missing from the geojson file, this adds it
and uses human-readable indents.

fixes #4112

[hughhhh]

🚢

[mjdepalma]

I tested this change with 0.22, but it unfortunately does not fix the problem. From what I can see, the issue is that the file does not use the official ISO 3166-2 codes as the old country map did. For example, the code being used for Georgia is GA rather than US-GA. The old map format worked with US-GA, but this one does not. If my assumption is correct that all codes need the country dash prefix, then I believe the only remaining change would be to add the "US-" in front of all ISO codes in the file. For reference, please see http://www.statemaster.com/graph/ide_iso_316_cod_sor_by_nam_sta-us-codes-sorted-name-states

[mistercrunch]

Yeah I have to admit I considered both options while writing the PR. I think it's much more common to have the 2-letter code in databases for US states, but it's true that ISO3166-2 has a US- prefix. I'll adapt this to match ISO3166-2