To overcome possible issue with auto backup on Android disable it for…

… now

Links from plugin description:
- https://developer.android.com/guide/topics/data/autobackup#EnablingAutoBackup
- mogol/flutter_secure_storage#13 (comment)

android/app/src/main/AndroidManifest.xml

@@ -14,6 +14,7 @@
          additional functionality it is fine to subclass or reimplement
          FlutterApplication and put your custom class here. -->
     <application
+        android:allowBackup="false"
         android:name="io.flutter.app.FlutterApplication"
         android:label="WebTrit"
         android:icon="@mipmap/ic_launcher">