Updated issue label names in CONTRIBUTING.md
Updated issue label names in CONTRIBUTING.md

Reflects label name change from https://github.com/AnalyticalGraphicsInc/cesium/issues/5902
soceur/cesium,hodbauer/cesium,kaktus40/cesium,YonatanKra/cesium,kaktus40/cesium,soceur/cesium,likangning93/cesium,progsung/cesium,AnalyticalGraphicsInc/cesium,jasonbeverage/cesium,josh-bernstein/cesium,likangning93/cesium,hodbauer/cesium,geoscan/cesium,CesiumGS/cesium,likangning93/cesium,CesiumGS/cesium,likangning93/cesium,YonatanKra/cesium,geoscan/cesium,jasonbeverage/cesium,AnalyticalGraphicsInc/cesium,CesiumGS/cesium,CesiumGS/cesium,progsung/cesium,josh-bernstein/cesium,hodbauer/cesium,CesiumGS/cesium,soceur/cesium,YonatanKra/cesium,YonatanKra/cesium,likangning93/cesium