Added bitmap-sdf to third party section of LICENSE.md
Added bitmap-sdf to third party section of LICENSE.md

progsung/cesium,likangning93/cesium,likangning93/cesium,CesiumGS/cesium,YonatanKra/cesium,YonatanKra/cesium,AnalyticalGraphicsInc/cesium,CesiumGS/cesium,likangning93/cesium,jasonbeverage/cesium,likangning93/cesium,YonatanKra/cesium,jasonbeverage/cesium,CesiumGS/cesium,CesiumGS/cesium,progsung/cesium,AnalyticalGraphicsInc/cesium,YonatanKra/cesium,likangning93/cesium,CesiumGS/cesium