loadURL not working for certain site



I’m trying to embed a website into electron. Works with some sites, but one does not (tiddlywiki, see code below). Tried to download the file and fix the first issue, but next issues were waiting…

The question: What’s the general problem with embedding this site?

Thanks in advance!

'use strict';

const electron = require('electron');
const app = electron.app;  // Module to control application life.
const BrowserWindow = electron.BrowserWindow;  // Module to create native browser window.

var mainWindow = null;

app.on('ready', function() {
   mainWindow = new BrowserWindow({
      width: 800,
      height: 600,
   // mainWindow.loadURL('file://' + __dirname + '/index.html'); // works
   mainWindow.loadURL('http://tiddlywiki.com/'); // fails