public BubbleChartValueFormatter getFormatter() {
        return formatter;
    }
Set bubble scale which is used to adjust bubble size. If you want smaller bubbles set scale {@code <0, 1>},
if you want bigger bubbles set scale greater than 1, default is 1.0f.
hellocharts-library/src/lecho/lib/hellocharts/model/BubbleChartData.java