Fix difference in translation strings regarding the new Between Two Seas map (#416)

##Description:
I renamed all instances of "TwoSeas" to "BetweenTwoSeas". That way it
lowers the confusion but more importrantly - it removes the difference
between the translation strings for the map.

Please put your Discord username so you can be contacted if a bug or
regression is found:

<Nikola123>

src/scripts/generateTerrainMaps.ts

@@ -19,7 +19,7 @@ const maps = [
   "Australia",
   "Pangaea",
   "Iceland",
-  "TwoSeas",
+  "BetweenTwoSeas",
   "Japan",
   "KnownWorld",
 ];