set compileSdkVersion 34 to fix build errors

Newer versions of Flutter require newer compileSdkVersion

Author: jkasten2

android/build.gradle

@@ -22,7 +22,7 @@ rootProject.allprojects {
 apply plugin: 'com.android.library'
 
 android {
-    compileSdkVersion 28
+    compileSdkVersion 34
     // Condition for namespace compatibility in AGP <4.2
     if (project.android.hasProperty("namespace")) {
         namespace 'com.onesignal.flutter'

example/android/app/build.gradle

@@ -15,7 +15,7 @@ apply plugin: 'com.android.application'
 apply from: "$flutterRoot/packages/flutter_tools/gradle/flutter.gradle"
 
 android {
-    compileSdkVersion 33
+    compileSdkVersion 34
 
     lintOptions {
         disable 'InvalidPackage'