updated WebMapTileServiceImageryProvider.js after meeting with Eli
updated WebMapTileServiceImageryProvider.js after meeting with Eli

likangning93/cesium,AnalyticalGraphicsInc/cesium,CesiumGS/cesium,AnalyticalGraphicsInc/cesium,CesiumGS/cesium,likangning93/cesium,CesiumGS/cesium,CesiumGS/cesium,likangning93/cesium,likangning93/cesium,CesiumGS/cesium,likangning93/cesium