Double wait time until quit

On my modern Macbook 12" I've run into "Saving state took too long.
Quitting.". We have users with spinning disk drives, so let's be a bit
more generous.

src/main/index.js

@@ -107,7 +107,7 @@ function init () {
     setTimeout(() => {
       console.error('Saving state took too long. Quitting.')
       app.quit()
-    }, 2000) // quit after 2 secs, at most
+    }, 4000) // quit after 4 secs, at most
   })
 
   app.on('activate', function () {