core: 修复一处category解析错误的问题

packages/hydrooj/package.json

@@ -1,6 +1,6 @@
 {
     "name": "hydrooj",
-    "version": "2.28.30",
+    "version": "2.28.31",
     "bin": "bin/hydrooj.js",
     "main": "dist/loader.js",
     "typings": "dist/loader.d.ts",

packages/hydrooj/src/handler/problem.ts

@@ -28,7 +28,7 @@ import {
     Route, Handler, Types, param, post, route, query,
 } from '../service/server';
 
-export const parseCategory = (value: string) => flatten(value.split('+').map((e) => e.split(','))).map((e) => e.trim());
+export const parseCategory = (value: string) => flatten(value.replace(/，/g, ',').split('+').map((e) => e.split(','))).map((e) => e.trim());
 export const parsePid = (value: string) => (isSafeInteger(value) ? +value : value);
 
 export class ProblemHandler extends Handler {