updated changelog to address PR feedback

com.unity.perception/CHANGELOG.md

 
 ### Changed
 
-Scenario JSON configurations that were generated using previous versions will need to be manually updated to reflect the following changes:
- - Changed the JSON serialization key of Normal Sampler's standard deviation property from "standardDeviation" to "stddev".
- - Changed the JSON serialization of randomizers in a scenario to an array of groups rather than a dictionary.
+Changed the JSON serialization key of Normal Sampler's standard deviation property from "standardDeviation" to "stddev".
+ 
+Changed the JSON serialization of Randomizers in a scenario to an array of groups rather than a dictionary.
 
 ### Deprecated