use "src:alt_label" in preference to "src:geom" when available

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PR to resolve issue outlined in whosonfirst-data/whosonfirst-data#1834

Use "src:alt_label" in preference to "src:geom" when available for geojson.source field in SQLite db.

I'm not quite sure what's preferable for the "source" column in the meta files so I kept them the same (using "src:geom") 🤷

related: pelias/docker#192

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Files are being regenerated now and I can confirm the Canada issue is resolved.

stat -c '%y' whosonfirst-data-admin-ca-latest.db
2020-05-02 14:10:44.486517697 +0200

sqlite3 whosonfirst-data-admin-ca-latest.db 'SELECT id, source, is_alt FROM geojson WHERE id = 85633041'
85633041|whosonfirst|0
85633041|naturalearth-display-terrestrial-zoom6|1
85633041|naturalearth|1
85633041|quattroshapes|1
85633041|whosonfirst-reversegeo|1

They're generated alphabetically and it's only up to 'S', so it'll take a while longer before the new files are uploaded.

[missinglink]

Assets have been uploaded