Added KHR_materials_pbrSpecularGlossiness to supported extensions
Added KHR_materials_pbrSpecularGlossiness to supported extensions

CesiumGS/cesium,progsung/cesium,geoscan/cesium,likangning93/cesium,YonatanKra/cesium,hodbauer/cesium,josh-bernstein/cesium,josh-bernstein/cesium,CesiumGS/cesium,soceur/cesium,geoscan/cesium,kaktus40/cesium,jasonbeverage/cesium,kaktus40/cesium,AnalyticalGraphicsInc/cesium,AnalyticalGraphicsInc/cesium,likangning93/cesium,YonatanKra/cesium,YonatanKra/cesium,jasonbeverage/cesium,likangning93/cesium,soceur/cesium,CesiumGS/cesium,likangning93/cesium,CesiumGS/cesium,YonatanKra/cesium,likangning93/cesium,hodbauer/cesium,hodbauer/cesium,CesiumGS/cesium,soceur/cesium,progsung/cesium