I was trouble with the bubble chart in high charts. i want to change grid line distance in x-axis

Question

https://jsfiddle.net/Kondaldurgam/459tsdjq/1/

I'm tried to do change in grid line distance in x-axis but i won't get exactly answer in my output .when i was applying in my project code it's not working properly

Highcharts.chart('container', {

chart: {
    type: 'bubble',
    plotBorderWidth: 1,
    zoomType: 'xy'
},

title: {
    text: 'Highcharts Bubbles'
},

xAxis: {
    gridLineWidth: 1,
},

yAxis: {
    startOnTick: false,
    endOnTick: false
},

series: [{
    data: [
        [9, 81, 63],
        [98, 5, 89],
        [51, 50, 73],
        [41, 22, 14],
        [58, 24, 20],
        [78, 37, 34],
        [55, 56, 53],
        [18, 45, 70],
        [42, 44, 28],
        [3, 52, 59],
        [31, 18, 97],
        [79, 91, 63],
        [93, 23, 23],
        [44, 83, 22]
    ]
  },]

});