allow alliance extension Fixes #491 (#1314)

## Description:

About 30s before an alliance is about to expire, both players receive a
prompt to extend the alliance. If both players agree the alliance is
extended.

## 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 understand that submitting code with bugs that could have been
caught through manual testing blocks releases and new features for all
contributors

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

evan

src/core/execution/PlayerExecution.ts

@@ -72,10 +72,7 @@ export class PlayerExecution implements Execution {
 
     const alliances = Array.from(this.player.alliances());
     for (const alliance of alliances) {
-      if (
-        this.mg.ticks() - alliance.createdAt() >
-        this.mg.config().allianceDuration()
-      ) {
+      if (alliance.expiresAt() <= this.mg.ticks()) {
         alliance.expire();
       }
     }