update android build

Frontend/android/.gitignore

@@ -5,9 +5,10 @@ gradle-wrapper.jar
 /gradlew.bat
 /local.properties
 GeneratedPluginRegistrant.java
+.cxx/
 
 # Remember to never publicly share your keystore.
-# See https://flutter.dev/docs/deployment/android#reference-the-keystore-from-the-app
+# See https://flutter.dev/to/reference-keystore
 key.properties
 **/*.keystore
 **/*.jks