Update example app on Flutter plugin (#220)

* Update example app on Flutter plugin

* Expose `empty_wallet_cache` through Dart bindings (#224)

packages/flutter/example/android/gradle.properties

@@ -1,3 +1,4 @@
 org.gradle.jvmargs=-Xmx1536M
 android.useAndroidX=true
 android.enableJetifier=true
+dev.steenbakker.mobile_scanner.useUnbundled=true

packages/flutter/example/android/settings.gradle

@@ -19,7 +19,8 @@ pluginManagement {
 plugins {
     id "dev.flutter.flutter-plugin-loader" version "1.0.0"
     id "com.android.application" version "7.1.2" apply false
-    id "org.jetbrains.kotlin.android" version "1.6.10" apply false
+    // mobile_scanner requires 1.7.20
+    id "org.jetbrains.kotlin.android" version "1.7.20" apply false
 }
 
 include ":app"