echars柱状图设置渐变色的时候提示 'LinearGradient未定义,请教大神怎么解决

//柱状图
                var option2 = {
                    backgroundColor: '#fbf4ec',
                    title: {
                        text: '资产分布',
                        x: '30',
                        textStyle: {
                            fontSize: 20,
                            fontWeight: 'bolder',
                            align: 'center'
                        }
                    },
                    animation: false,
                    grid: {
                        show: 'true',
                        borderWidth: '0'
                    },
                    calculable: false,
                    yAxis: [{
                        axisLine: {
                            show: false
                        },
                        axisTick: {
                            show: false
                        },
                        axisLabel: {
                            show: true
                        },
                        type: 'category',
                        boundaryGap: false,
                        splitLine: {
                            show: false
                        },
                        data: ['100万以上','50~100万', '10~50万', '5~10万','1~5万', '0~1万']
                    }],
                    xAxis: [{
                        type: 'value',
                        nameLocation: 'end',
                        show: false,
                        splitLine: {
                            show: false
                        },
                        splitArea: {
                            show: false
                        },                        axisTick: {
                            show: false
                        }
                    }],
                    series: [
                        {
                            name: '',
                            type: 'bar',
                            barWidth: '30',
                            barGap: '25',
                            itemStyle: {
                                normal: {
                                    color: new echarts.graphic.LinearGradient(0, 0, 0, 1, [{
                                        offset: 0,
                                        color: '#99d9ea'
                                    }, {
                                        offset: 1,
                                        color: '#3fa7dc'
                                    }]),
                                   
                                }
                            },
                            data: [that.zichan6, that.zichan5, that.zichan4,that.zichan3, that.zichan2, that.zichan1]
                        }]
                };