build: bump version to 1.3.0

- Update version in pubspec.yaml from 1.2.1 to 1.3.0

Author: fulleni

pubspec.yaml

@@ -1,6 +1,6 @@
 name: flutter_news_app_mobile_client_full_source_code
 description: Complete, production-ready source code for a feature-rich Flutter news app mobile client.
-version: 1.2.1
+version: 1.3.0
 publish_to: none
 repository: https://github.com/flutter-news-app-full-source-code/flutter-news-app-mobile-client-full-source-code
 homepage: https://flutter-news-app-full-source-code.github.io/docs/