Added reference on winner

lib/data/db/tables/game_table.dart

@@ -1,10 +1,11 @@
 import 'package:drift/drift.dart';
+import 'package:game_tracker/data/db/tables/player_table.dart';
 
 class GameTable extends Table {
   TextColumn get id => text()();
   TextColumn get name => text()();
-  // todo: winner id needs to be deleted when corresponding player gets deleted
-  TextColumn get winnerId => text().nullable()();
+  TextColumn get winnerId =>
+      text().references(PlayerTable, #id, onDelete: KeyAction.cascade)();
 
   @override
   Set<Column<Object>> get primaryKey => {id};