Another small doc fix
Another small doc fix

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