Lock OneSignal Android Version

This prevents it from being bumped by EDM4U which can cause
unpredictable behavior.

This resolves #573 which was due to EDM4U bumping to the major 5.0.0
version of OneSignal which has breaking API changes.

Author: jkasten2

OneSignalExample/Assets/OneSignal/CHANGELOG.md

@@ -5,6 +5,8 @@ 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]
+### Fixed
+- Android - Lock OneSignal version so it doesn't get bumped to the next major version.
 ## [3.0.8]
 ### Changed
 - Renamed `enterLiveActivity` to `EnterLiveActivity` and `exitLiveActivity` to `ExitLiveActivity`

com.onesignal.unity.android/Editor/OneSignalAndroidDependencies.xml

@@ -3,6 +3,6 @@
     <repositories>
       <repository>https://repo.maven.apache.org/maven2</repository>
     </repositories>
-    <androidPackage spec="com.onesignal:OneSignal:4.8.3" />
+    <androidPackage spec="com.onesignal:OneSignal:[4.8.3]" />
   </androidPackages>
 </dependencies>