core: add missing export for ScheduleModel

packages/hydrooj/src/plugin-api.ts

@@ -28,6 +28,7 @@ export { default as TokenModel } from './model/token';
 export { default as UserModel } from './model/user';
 export { default as ProblemModel } from './model/problem';
 export { default as RecordModel } from './model/record';
+export { default as ScheduleModel } from './model/schedule';
 export { default as SolutionModel } from './model/solution';
 export { default as MessageModel } from './model/message';
 export { default as OauthModel } from './model/oauth';