public void setMinBubbleRadius(int minBubbleRadius) {
        this.minBubbleRadius = minBubbleRadius;
    }
Set minimal bubble radius in dp, helpful when you want small bubbles(bubbles with very small z values compared to
other bubbles) to be visible on chart, default 6dp
hellocharts-library/src/lecho/lib/hellocharts/model/BubbleChartData.java