【问题原因】polygonEntity需要设置outline=true，才能显示轮廓
【解决办法】安装如下代码设置polygonEntity样式：
var handler = new Cesium.DrawHandler(viewer,Cesium.DrawMode.Polygon);
handler.drawEvt.addEventListener(function(res){
viewer.entities.removeById(handler.polyline.id);
var polygonEntity = res.object.polygon;
polygonEntity.outline=true;
polygonEntity.outlineColor = new Cesium.Color(1, 1, 0, 1);
polygonEntity.outlineWidth =1;
polygonEntity.material.color = new Cesium.Color(1, 0, 0, 0.6);
});
handler.activate();
