ui: writable stream for ff (#146)

packages/ui-default/package.json

@@ -1,6 +1,6 @@
 {
   "name": "@hydrooj/ui-default",
-  "version": "4.8.44",
+  "version": "4.8.45",
   "author": "undefined <i@undefined.moe>",
   "license": "AGPL-3.0",
   "main": "hydro.js",

packages/ui-default/pages/problem_main.page.js

@@ -1,3 +1,4 @@
+import { WritableStream } from 'web-streams-polyfill/dist/ponyfill.es6';
 import _ from 'lodash';
 import { dump } from 'js-yaml';
 import * as streamsaver from 'streamsaver';