chore: edit doc comment in auth_plugin_impl

Author: khatruong2009

packages/auth/amplify_auth_cognito_dart/lib/src/auth_plugin_impl.dart

@@ -885,8 +885,8 @@ class AmplifyAuthCognitoDart extends AuthPluginInterface
   /// {@template amplify_core.amplify_auth_category.update_mfa_preference}
   /// Updates the MFA preference for the current user.
   ///
-  /// If [sms] or [totp] is `null`, the preference for that MFA type is left
-  /// unchanged. Setting either [sms] or [totp] to [MfaPreference.preferred]
+  /// If [sms], [totp], or [email] is `null`, the preference for that MFA type is left
+  /// unchanged. Setting either [sms], [totp], or [email] to [MfaPreference.preferred]
   /// will mark the other as not preferred.
   /// {@endtemplate}
   Future<void> updateMfaPreference({