Autoupdate fails to install the deb version at least on WSL

[Jaifroid]

Support for deb auto-updating is experimental in Electron Builder (it has only recently been introduced). However, on WSL at least, after downloading the update and telling the user to re-launch, an attempt is made to install the update, but nothing in fact happens. On re-launching the app, it is not updated. It detects the download succeeded correctly, and again tells the user to re-launch to update the app.

[Jaifroid]

While this should be fixed in Electron Builder, we could either block the autoupdate download, or else instruct users on how to install the downloaded file manually.