hotfix: remove -rc1 suffix from version 6.17.8 (#432)

Version in pubspec.yaml was incorrectly merged with RC suffix.
This fixes the version to be production-ready.

Author: Dani-Koza-AF

pubspec.yaml

@@ -1,6 +1,6 @@
 name: appsflyer_sdk
 description: A Flutter plugin for AppsFlyer SDK. Supports iOS and Android.
-version: 6.17.8-rc1
+version: 6.17.8
 
 homepage: https://github.com/AppsFlyerSDK/flutter_appsflyer_sdk