URL_CONFIG这些都是对的但是就是显示不出来,也不报错,是不是需要引用啥
 //初始化viewer部件
        var viewer = new Cesium.Viewer('cesiumContainer');
        viewer.imageryLayers.addImageryProvider(new Cesium.BingMapsImageryProvider({
            url : '
https://dev.virtualearth.net',
            mapStyle : Cesium.BingMapsStyle.AERIAL,
            key : URL_CONFIG.BING_MAP_KEY
        }));