Amend Android build settings (#19)

Author: thermitex

android/app/build.gradle

@@ -45,7 +45,7 @@ android {
         applicationId "xyz.hku.cuckoo"
         // You can update the following values to match your application needs.
         // For more information, see: https://docs.flutter.dev/deployment/android#reviewing-the-gradle-build-configuration.
-        minSdkVersion flutter.minSdkVersion
+        minSdkVersion 21
         targetSdkVersion flutter.targetSdkVersion
         versionCode flutterVersionCode.toInteger()
         versionName flutterVersionName

android/settings.gradle

@@ -20,7 +20,7 @@ pluginManagement {
 plugins {
     id "dev.flutter.flutter-plugin-loader" version "1.0.0"
     id "com.android.application" version "7.3.0" apply false
-    id "org.jetbrains.kotlin.android" version "1.7.10" apply false
+    id "org.jetbrains.kotlin.android" version "1.9.0" apply false
 }
 
 include ":app"