如何使我的区域花线高图角弯曲

Question

在下面的示例中，灰色正方形区域是现有贷款，天蓝色区域是新的贷款。在此图表中，我们总共有3个角。我的要求是看到所有三个角都弯曲而不实际修改/影响X轴上的实际日期。提前致谢。

https://jsfiddle.net/y0kqsrav/183/

Highcharts.chart('container', {
    chart: {
        type: 'areaspline'
    },
    title: {
        text: 'Credit Loan'
    },
    subtitle: {
        text: 'New/Existing Loans'
    },
    xAxis: {

            title: '',
            type: 'datetime',
                        labels: {
              format: '{value:%d.%m.%y}'
              }
    },
    yAxis: {
        title: {
            text: 'millions'
        },
        labels: {
            formatter: function () {
                return this.value/1000000;
            }
        }
    },
    tooltip: {
        split: true,
        valueSuffix: ' millions'
    },
    plotOptions: {
        areaspline: {

    //        stacking: 'areaspline',

            lineColor: '#666666',
            lineWidth: 1,
            marker: {
                lineWidth: 1,
                lineColor: '#666666',

            }
        }
    },
    series: [{
        name: 'New Loan',

        data: [
        [Date.UTC(2018, 6,  7), 155317288],
        [Date.UTC(2018, 11,  29), 155317288],
        [Date.UTC(2018, 11,  29), 80000000],
        [Date.UTC(2019, 5,  6), 80000000],

        ]
    },
    {
        name: 'Existing Loan',
        data: [
        [Date.UTC(2018, 6,  7), 75317288],
        [Date.UTC(2018, 11,  29), 75317288],        

        ]
    }]
});
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