Update CHANGES.md

Author: lilleyse

CHANGES.md

@@ -4,12 +4,12 @@ Change Log
 ### 1.56 - 2019-04-01
 
 ##### Fixes :wrench:
-* Fixed the value for `BlendFunction.ONE_MINUS_CONSTANT_COLOR`.
+* Fixed the value for `BlendFunction.ONE_MINUS_CONSTANT_COLOR`. [#7624](https://github.com/AnalyticalGraphicsInc/cesium/pull/7624)
 
 ### 1.55 - 2019-03-01
 
 ##### Breaking Changes :mega:
-* `czm_materialInput.slope` is now an angle in radians between 0 and pi/2 (flat to vertical), rather than a projected length 1 to 0 (flat to vertical).
+* `czm_materialInput.slope` is now an angle in radians between 0 and pi/2 (flat to vertical), rather than a projected length 1 to 0 (flat to vertical). [#7624](https://github.com/AnalyticalGraphicsInc/cesium/pull/7624)
 
 ##### Additions :tada:
 * Updated terrain and imagery rendering, resulting in terrain/imagery loading ~33% faster and using ~33% less data [#7061](https://github.com/AnalyticalGraphicsInc/cesium/pull/7061)