message: fix(GUI): correctly reference the `eta` property in `lib/gui/app.js`
  See:
diff: @@ -140,7 +140,7 @@ app.run((AnalyticsService, OSWindowProgressService) => {
  //
  // We use the presence of `.eta` to determine that the actual
  // writing started.
  - if (!flashState.isFlashing() || !flashState.eta) {
  + if (!flashState.isFlashing() || !currentFlashState.eta) {
  return;
  }
  