added myself to CONTRIBUTORS
added myself to CONTRIBUTORS

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