Support upcoming Electron 5.0 with nodeIntegration disabled by default

[miniak]

Electron 5.0 is going to have nodeIntegration disabled by default (electron/electron#16235).

need to replace

mainWindow = new BrowserWindow({width: 800, height: 600})

with

mainWindow = new BrowserWindow({
  width: 800,
  height: 600,
  webPreferences: {
    nodeIntegration: true
  }
})

[malept]

Seems like by default all of the examples should be nodeIntegration = false, and maybe there should be a "Show Me ➡️ Electron APIs ➡️ Node Integration" example.