add namespace

Author: SelaseKay

packages/firebase_snippets_app/android/app/build.gradle

@@ -27,6 +27,7 @@ apply plugin: 'kotlin-android'
 apply from: "$flutterRoot/packages/flutter_tools/gradle/flutter.gradle"
 
 android {
+    namespace = "com.example.firebase_snippets_app"
     compileSdkVersion flutter.compileSdkVersion
 
     compileOptions {