Update CHANGELOG.md for 5.1.16

Author: github-actions[bot]

OneSignalExample/Assets/OneSignal/CHANGELOG.md

@@ -5,6 +5,10 @@ The format is based on [Keep a Changelog](https://keepachangelog.com/en/1.0.0/),
 and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0.html).
 
 ## [Unreleased]
+## [5.1.16]
+### Changed
+
+
 ## [5.1.15]
 ### Changed
 - Updated included Android SDK from 5.1.31 to [5.1.37](https://github.com/OneSignal/OneSignal-Android-SDK/releases/tag/5.1.37)