Android build warning

[behnamsattar]

Based on the warning message I got while building for Android, this package uses deprecated API.

Note: /Users/behnam/.pub-cache/hosted/pub.dev/fk_user_agent-2.1.0/android/src/main/java/io/flutterfastkit/fk_user_agent/FkUserAgentPlugin.java uses or overrides a deprecated API.