Update CHANGELOG.md

Author: minbi

CHANGELOG.md

@@ -19,6 +19,7 @@
 * Model updates for the following services
   * AWS Autoscaling
   * Amazon Cognito Identity
+  * Amazon Cognito Identity Provider
   * Amazon Kinesis Video
 
 ## [Release 2.12.6](https://github.com/aws/aws-sdk-android/releases/tag/release_v2.12.6)