Have trains produce more gold (#1759)

## Description:

During the play test, trains did not produce enough gold. So increase
gold, and give 4x bonus for allies.

## Please complete the following:

- [x] I have added screenshots for all UI updates
- [x] I process any text displayed to the user through translateText()
and I've added it to the en.json file
- [x] I have added relevant tests to the test directory
- [x] I confirm I have thoroughly tested these changes and take full
responsibility for any bugs introduced
- [x] I have read and accepted the CLA agreement (only required once).

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

evan

src/core/configuration/Config.ts

@@ -130,7 +130,7 @@ export interface Config {
   unitInfo(type: UnitType): UnitInfo;
   tradeShipGold(dist: number, numPorts: number): Gold;
   tradeShipSpawnRate(numberOfPorts: number): number;
-  trainGold(): Gold;
+  trainGold(isFriendly: boolean): Gold;
   trainSpawnRate(numberOfStations: number): number;
   trainStationMinRange(): number;
   trainStationMaxRange(): number;