amcharts4 grid line should hide beyond baseLine i.e 0

Question

plz click here to check the image want to show the bubble but hide the grid line.

<script src="https://www.amcharts.com/lib/4/core.js"></script>
<script src="https://www.amcharts.com/lib/4/charts.js"></script>
<script src="https://www.amcharts.com/lib/4/themes/animated.js"></script>
<div id="chartdiv"></div>
<!-- Chart code -->
<script>
    // Themes begin
    am4core.useTheme(am4themes_animated);
    // Themes end

    // Create chart instance
    var chart = am4core.create("chartdiv", am4charts.XYChart);
    chart.colors.step = 3;

    // Add data
    chart.data = [  {
      "y": 5,
      "x": 3,
      "value": 50,
      "y2": 15,
      "x2": 8,
      "value2": 12
    }, {
      "y": 10,
      "x": 8,
      "value": 19,
      "y2": 4,
      "x2": 6,
      "value2": 35
    }, {
      "y": 15,
      "x": 4,
      "value": 92,
      "y2": 10,
      "x2": 8,
      "value2": 102
    }, {
      "y": 13,
      "x": 1,
      "value": 8,
      "y2": 2,
      "x2": 0,
      "value2": 41
    }, {
      "y": 1,
      "x": 6,
      "value": 35,
      "y2": 0,
      "x2": 3,
      "value2": 16
    } ];

    // Create axes
    var xAxis = chart.xAxes.push(new am4charts.ValueAxis());
    xAxis.renderer.minGridDistance = 50;

    var yAxis = chart.yAxes.push(new am4charts.ValueAxis());
    yAxis.renderer.minGridDistance = 50;
    chart.maskBullets = true;
    yAxis.paddingBottom = 10;
    // Create series #1
    var series = chart.series.push(new am4charts.LineSeries());
    series.dataFields.valueY = "y";
    series.dataFields.valueX = "x";
    series.dataFields.value = "value";
    series.strokeOpacity = 0;
    series.name = "Series 1";

    var bullet = series.bullets.push(new am4charts.CircleBullet());
    bullet.strokeOpacity = 0.2;
    bullet.stroke = am4core.color("#ffffff");
    bullet.nonScalingStroke = true;
    bullet.tooltipText = "x:{valueX} y:{valueY}";
    series.heatRules.push({
      target: bullet.circle,
      min: 10,
      max: 60,
      property: "radius"
    });

    // Create series #2
    var series2 = chart.series.push(new am4charts.LineSeries());
    series2.dataFields.valueY = "y2";
    series2.dataFields.valueX = "x2";
    series2.dataFields.value = "value2";
    series2.strokeOpacity = 0;
    series2.name = "Series 2";

    var bullet2 = series2.bullets.push(new am4charts.Bullet());
    bullet2.tooltipText = "x:{valueX} y:{valueY}";
    bullet2.layout = "absolute";
    bullet2.rotation = 45;

    var rectangle = bullet2.createChild(am4core.Rectangle);
    rectangle.verticalCenter = "middle";
    rectangle.horizontalCenter = "middle";
    rectangle.width = 10;
    rectangle.height = 10;
    rectangle.strokeOpacity = 0.5;
    rectangle.stroke = am4core.color("#ffffff");
    rectangle.nonScalingStroke = true;

    rectangle.verticalCenter = "middle";
    rectangle.horizontalCenter = "middle";

    series2.heatRules.push({
      target: rectangle,
      min: 1,
      max: 8,
      property: "scale"
    });

    chart.scrollbarX = new am4core.Scrollbar();
    chart.scrollbarY = new am4core.Scrollbar();

    chart.legend = new am4charts.Legend();
</script>
<div id="chartdiv"></div>

Grid line(y-axis)is going beyond x-axis as i have given paddingBottom for yAxis.i tried giving maskBullet = false, but when i scroll bubbles will go out of chart. So i tried giving padding bottom to show the bubbles which lay on x axis 0 value