message: fix(GUI): send an "elevation cancelled" analytics event
  If the user cancels the elevation dialog, then no event is emitted,
  making it hard to track down what happened after the flash button was
  pressed.
diff: @@ -68,6 +68,10 @@ module.exports = function(
  ImageWriterService.flash(image.path, drive).then(() => {
  if (flashState.wasLastFlashCancelled()) {
  + AnalyticsService.logEvent('Elevation cancelled', {
  + image,
  + drive
  + });
  return;
  }
  