graphic的type为group时，设置draggable:true，不能拖拽echarts 配置项内容和展示

      option = {
    graphic: [{
        type: 'group',
        id: 'textGroup2',
        left: 100,
        top: 100,
        draggable:true,
        children: [
            {
                type: 'rect',
                z: 100,
                left: 'center',
                top: 'center',
                shape: {
                    width: 330,
                    height: 100
                },
                style: {
                    fill: '#fff',
                    stroke: '#999',
                    lineWidth: 2,
                    shadowBlur: 8,
                    shadowOffsetX: 3,
                    shadowOffsetY: 3,
                    shadowColor: 'rgba(0,0,0,0.3)'
                }
            },
            {
                type: 'text',
                z: 100,
                top: 'middle',
                left: 'center',
                style: {
                    text: [
                        '这个文本框的 bounding 为 "all"',
                        '表示定位时取整个 group 的',
                        '经过 transform 后的包围盒。'
                    ].join('\n'),
                    font: '20px "STHeiti", sans-serif'
                }
            }
        ]
    }]
}