echars2.0中lengend图标不是圆形，是方形，怎么修改为圆echarts 饼配置项内容和展示

echars2.0中lengend图标不是圆形，是方形，怎么修改为圆

      option = {
  color: ["#ff1409","#ffa800","#ffe71c","#7e55f9"],
				 
			    title : {
			        text: '危险程度评估情况',
			        textStyle: {
			            color: "rgb(255, 0, 0)",
			            fontSize: 20,
			            fontStyle: "normal",
			            fontWeight: "bold"
			        },
			        padding:10,
			        x:'center'
			    },
			    tooltip: {
			    	backgroundColor:"rgba(0,0,0,0)",
			        trigger: "item",
			        formatter: "{b}<br>  {d}%",
			        textStyle: {
			            color: "rgb(255,0, 0)",
			            fontSize: 14
			        }
			    },
			   
			    legend: {
			        x: "center",
			        data:[
			            {
			                name:'极高',
			                icon:'emptyCircle'
			            },
			            {
			                name:'高度',
			                icon:'circle'
			            },
			            {
			                name:'中度',
			                icon:'circle'
			            },
			            {
			                name:'低度',
			                icon:'circle',
			            }
			       
			        ],
			        orient: "horizontal",
			        y: "bottom",
			        itemGap:24,
			        padding:10,
			        itemWidth: 8,
			        itemHeight: 8,
			        
			        textStyle: {
					    color: "#ff0000",
					    fontSize: 13,
					    fontStyle: "normal"
					    }
			    },
			    series: [
			        {
			            type:'pie',
			            radius: ['55px', '69px'],
			    		itemStyle: {
			                normal: {
			                    label: {
			                        show: true,
			                    },
			                    labelLine: {
			                        show: true,
			                        color: "rgb(255, 0, 0)"
			                    }
			                }
			            },
			              
			            data:[
			                {value:335, name:'极高'},
			                {value:310, name:'高度'},
			                {value:234, name:'中度'},
			                {value:135, name:'低度'},
			               
			            ]
			        }
			    ],
			    
			};