Resolve "Upgrade Android Gradle Plugin"

Closes #27 (closed)

android/app/build.gradle

@@ -13,7 +13,7 @@ if (keystorePropertiesFile.exists()) {
 android {
     namespace = "org.benoitharrault.midisynth"
     compileSdk = flutter.compileSdkVersion
-    ndkVersion = flutter.ndkVersion
+    ndkVersion = "27.0.12077973"
 
     compileOptions {
         sourceCompatibility = JavaVersion.VERSION_1_8