Small fix for Readme: SpeedometerView.LabelConverter() - cannot resolve SpeedometerView

[anonym24]

From Readme:

// Add label converter
  speedometer.setLabelConverter(new SpeedometerView.LabelConverter() {
      @Override
      public String getLabelFor(double progress, double maxProgress) {
          return String.valueOf((int) Math.round(progress));
      }
  });

I guess it should benew SpeedometerGauge.LabelConverter()