core: fix ts types import

packages/hydrooj/src/model/schedule.ts

@@ -5,6 +5,7 @@ import { Context } from '../context';
 import { Schedule } from '../interface';
 import { Logger } from '../logger';
 import db from '../service/db';
+import { } from '../service/worker';
 import RecordModel from './record';
 
 const logger = new Logger('model/schedule');