chore: replace broken naturalearthdata.com URL with github links

rebuild.sh

@@ -2,13 +2,18 @@
 set -ex
 
 # Latest release is here: https://github.com/evansiroky/timezone-boundary-builder/releases
-TZ="2023d"
+TZ="2024a"
 
 rm -rf timezones.geojson.zip dist ne_10m_urban_areas.*
 curl -L --retry 3 -C - \
   -O "https://github.com/evansiroky/timezone-boundary-builder/releases/download/$TZ/timezones.geojson.zip" \
-  -O 'https://www.naturalearthdata.com/http//www.naturalearthdata.com/download/10m/cultural/ne_10m_urban_areas.zip'
+  -O "https://raw.githubusercontent.com/nvkelso/natural-earth-vector/master/10m_cultural/ne_10m_urban_areas.shp" \
+  -O "https://raw.githubusercontent.com/nvkelso/natural-earth-vector/master/10m_cultural/ne_10m_urban_areas.shx"
+
+# Expected sha256sums:
+# 76b8c5786af5df4fa18ae615e594347fb464525347038b15f9df15d1396cb7de  ne_10m_urban_areas.shp
+# d387658168a5974d5c8b858af2220c0fdcdfa5b69646d36839e358519816140e  ne_10m_urban_areas.shx
+
 unzip -u timezones.geojson.zip
-unzip -u ne_10m_urban_areas.zip
 ogr2ogr -f GeoJSON ne_10m_urban_areas.json ne_10m_urban_areas.shp
 node pack.js | ./node_modules/.bin/uglifyjs -mc >tz.js