Add PR link in CHANGES.md entry.
Add PR link in CHANGES.md entry.

Co-authored-by: Sean Lilley <c2796470ac2eef955bfd5ea34e81a156bd0b8d73@gmail.com>
CesiumGS/cesium,CesiumGS/cesium,progsung/cesium,AnalyticalGraphicsInc/cesium,AnalyticalGraphicsInc/cesium,likangning93/cesium,likangning93/cesium,CesiumGS/cesium,likangning93/cesium,CesiumGS/cesium,progsung/cesium,likangning93/cesium,likangning93/cesium,CesiumGS/cesium