message: fix a build warning
diff: @@ -60,8 +60,9 @@ protected:
  mView->setScene(mScene);
  mView->setCamera(mCamera);
  + LinearToneMapper linearToneMapper;
  mColorGrading = ColorGrading::Builder()
  - .toneMapping(ColorGrading::ToneMapping::LINEAR)
  + .toneMapper(&linearToneMapper)
  .build(*mEngine);
  mView->setColorGrading(mColorGrading);
  