饼图tooltip显示问题echarts 饼配置项内容和展示

使用dataset展示饼图，tooltip显示错误

      option = {
    title: {
        text: '饼图tooltip显示问11题'
    },
    tooltip:{
				trigger: 'item',
		        formatter: "{a} <br/>{b}: {c} ({d}%)"
			},
    dataset:{
        source:[
        {'ziyuan':'学习资讯','shuliang':100},
        {'ziyuan':'生活常识','shuliang':50},
        {'ziyuan':'世界历史','shuliang':160},
        {'ziyuan':'军事','shuliang':25},
        {'ziyuan':'医学','shuliang':48}
        ]
    },
    series: [{
       name:'数量',
	   type:'pie',
	   radius:'80%',
	   center:['50%', '50%']
    }]
};