Synchronous XMLHttpRequest on the main thread is deprecated (jQuery)

In index.html:
```
jquery-2.1.4.js:8561 Synchronous XMLHttpRequest on the main thread is deprecated because of its detrimental effects to the end user's experience. For more help, check https://xhr.spec.whatwg.org/.send @ jquery-2.1.4.js:8561
```

This is upstream issue. Maybe I should open it upstream, but maybe upstream uses older jQuery so it would be a problem only here.