locations: Correct AoE timezone

Etc/UTC-12 does not exist in tzdata, it's called Etc/GMT-12.
This fixes an error in gnome-clocks:
org.gnome.Clocks-WARNING **: world.vala:271: Timezone not defined for (null). This is a bug in libgweather database

https://bugzilla.gnome.org/show_bug.cgi?id=791307