CHANGELOG.md update

Author: uerceg

CHANGELOG.md

@@ -4,6 +4,9 @@
 - Added more aggressive sending retry logic for install session package.
 - Added additional parameters to `ad_revenue` package payload.
 
+#### Changed
+- Built this SDK version with `Unity 2017.4.1`.
+
 #### Native SDKs
 - [[email protected]][ios_sdk_v4.21.0]
 - [[email protected]][android_sdk_v4.21.0]