Update app ready wait for Electron 13

[scowalt]

I was upgrading an Electron app from version 12.2.1 to 13.5.1. I noticed some issues with the next-electron-server not starting. After some investigation, I was able to fix the issue locally by using app.whenReady() instead of app.once("ready").

I'm not 100% sure why this fix works, or why Electron 13 broke it! From the description of app.whenReady() in the Electron docs, it seems like this is its intended use:

Returns Promise<void> - fulfilled when Electron is initialized. May be used as a convenient alternative to checking app.isReady() and subscribing to the ready event if the app is not ready yet.

Maybe in Electron 13 you can't register app.once if the app isn't ready yet?

[HaNdTriX]

Thanks!