I have created a repository using GitHub for Windows (GfW) and added 3 commits and synced using aforementioned. Commits were visible on GitHub webpage and in my app. Then my brother forked my project to start collaborating with me. He successfully cloned it using GfW. Then i made changes on my machine and pushed using "sync" button. Changes appeared on webpage and in my history, but my brother can't see them in his GfW. Even after pressing "sync". What mistake are we making?