Simulation in slow motion when out of focus in Safari

In WebKit-based browsers like Safari or GNOME Web, the simulator turns much slower when it leaves the browser's visible area.

To reproduce the issue, loop some audio on the [demo page](https://python-simulator.usermbit.org/v/0.1/demo.html) and scroll down with a sufficient zoom level to get the simulator out of focus.

```python
import music

while True:
    music.play(music.PYTHON)
```