请问在多条折线情况下如何保证tooltip不被外层div遮挡echarts 折线配置项内容和展示

如图表中“周二”数据的tooltip上部分被遮挡住，请问如何调整tooltip跟随鼠标移动，且不被遮挡（2.0的版本可以实现）

      option = {
    title: {
        text: '未来一周气温变化',
        subtext: '纯属虚构'
    },
    tooltip: {
        trigger: 'axis',
        position: function (point, params, dom) {
              // 固定在顶部
              return [point[0], 20];
        }
    },
    legend: {
        data:['最高气温','最低气温','1','2','3','4','5','6','7','8','9','10','11','12','13','14','15','16','17','18','19','20','21','22','23','24','25','26','27','28','29','30','31','32','33','34','35','36','37','38','39','40']    },
    toolbox: {
        show: true,
        feature: {
            dataZoom: {
                yAxisIndex: 'none'
            },
            dataView: {readOnly: false},
            magicType: {type: ['line', 'bar']},
            restore: {},
            saveAsImage: {}
        }
    },
    xAxis:  {
        type: 'category',
        boundaryGap: false,
        data: ['周一','周二','周三','周四','周五','周六','周日']
    },
    yAxis: {
        type: 'value',
        axisLabel: {
            formatter: '{value} °C'
        }
    },
    series: [
        {
            name:'最高气温',
            type:'line',
            data:[11, 11, 15, 13, 12, 13, 10]
        },
        {
            name:'最低气温',
            type:'line',
            data:[1, -2, 2, 5, 3, 2, 0]
        },{
            name:'1',
            type:'line',
            data:[11, 1, 15, 13, 12, 13, 10]
        },{
            name:'2',
            type:'line',
            data:[11, 2, 15, 13, 12, 13, 10]
        },{
            name:'3',
            type:'line',
            data:[11, 11, 15, 13, 12, 13, 10]
        },{
            name:'4',
            type:'line',
            data:[11, 3, 15, 13, 12, 13, 10]
        },{
            name:'5',
            type:'line',
            data:[11, 4, 15, 13, 12, 13, 10]
        },{
            name:'6',
            type:'line',
            data:[11, 5, 15, 13, 12, 13, 10]
        },{
            name:'7',
            type:'line',
            data:[11, 6, 15, 13, 12, 13, 10]
        },{
            name:'8',
            type:'line',
            data:[11, 7, 15, 13, 12, 13, 10]
        },{
            name:'9',
            type:'line',
            data:[11, 8, 15, 13, 12, 13, 10]
        },{
            name:'10',
            type:'line',
            data:[11, 9, 15, 13, 12, 13, 10]
        },{
            name:'11',
            type:'line',
            data:[11, 10, 15, 13, 12, 13, 10]
        },{
            name:'12',
            type:'line',
            data:[11, 11, 15, 13, 12, 13, 10]
        },{
            name:'13',
            type:'line',
            data:[11, 11, 15, 13, 12, 13, 10]
        },{
            name:'14',
            type:'line',
            data:[11, 11, 15, 13, 12, 13, 10]
        },{
            name:'16',
            type:'line',
            data:[11, 6, 15, 13, 12, 13, 10]
        },{
            name:'15',
            type:'line',
            data:[11, 11, 15, 13, 12, 13, 10]
        },{
            name:'17',
            type:'line',
            data:[11, 11, 15, 13, 12, 13, 10]
        },{
            name:'18',
            type:'line',
            data:[11, 11, 15, 13, 12, 13, 10]
        },{
            name:'19',
            type:'line',
            data:[11, 11, 15, 13, 12, 13, 10]
        },{
            name:'20',
            type:'line',
            data:[11, 11, 15, 13, 12, 13, 10]
        },{
            name:'21',
            type:'line',
            data:[11, 11, 15, 13, 12, 13, 10]
        },{
            name:'22',
            type:'line',
            data:[11, 11, 15, 13, 12, 13, 10]
        }
    ]
};