Update Gradle Plugins

Update AGP,  Google Services, and the OneSignal Gradle plugins to the
latest verions.
Note that AGP (Android Gradle Plugin) 7 requires Java 11. This ships
with Android Studio 2020

Author: jkasten2

Examples/OneSignalDemo/build.gradle

@@ -7,9 +7,9 @@ buildscript {
         gradlePluginPortal()
     }
     dependencies {
-        classpath 'com.android.tools.build:gradle:3.5.0'
-        classpath 'com.google.gms:google-services:4.2.0'
-        classpath 'gradle.plugin.com.onesignal:onesignal-gradle-plugin:[0.11.0, 0.99.99]'
+        classpath 'com.android.tools.build:gradle:7.0.4'
+        classpath 'com.google.gms:google-services:4.3.10'
+        classpath 'gradle.plugin.com.onesignal:onesignal-gradle-plugin:[0.14.0, 0.99.99]'
 
         // TODO: Do not place your application dependencies here; they belong
         //  in the individual module build.gradle files