Electron example never finishes loading

### Bug Description:
I'm trying to run the electron example on my machine, but even from a clean clone and build it just gets stuck at a loading screen forever with no apparent errors anywhere:


### Steps to Reproduce:

From Developing.md:

```
git clone https://github.com/eclipse-theia/theia \
&& cd theia \
&& yarn \
&& yarn run rebuild:electron \
&& cd examples/electron \
&& yarn run start
```

### Additional Information

While the electron example gets stuck, the browser example works fine. I tried the same steps but first checked out v1.1.0, and the issue still happens.

Here's the logs from start to finish: https://pastebin.com/xU44UViN

- Operating System: Arch Linux
- Theia Version: master - bb43e9e
- Node Version: v10.20.1