message: feat(GUI): add a validateWriteOnSuccess property to the flash event
  This event property will allow us to inspect how many people are running
  Etcher without the validation mechanism.
  See:
diff: @@ -63,7 +63,8 @@ module.exports = function(
  AnalyticsService.logEvent('Flash', {
  image,
  drive,
  - unmountOnSuccess: settings.get('unmountOnSuccess')
  + unmountOnSuccess: settings.get('unmountOnSuccess'),
  + validateWriteOnSuccess: settings.get('validateWriteOnSuccess')
  });
  ImageWriterService.flash(image.path, drive).then(() => {
  