$ git subtree push --prefix src origin gh-pages
git push using: origin gh-pages
To https://github.com/nirajd24/BootstrapPortfolioProject.git
! [rejected] 1101aefaaa9185272dde8b7922a3e5ea51a4e723 -> gh-pages (non-fast-forward)
error: failed to push some refs to 'https://github.com/nirajd24/BootstrapPortfolioProject.git'
hint: Updates were rejected because the tip of your current branch is behind
hint: its remote counterpart. Integrate the remote changes (e.g.
hint: 'git pull ...') before pushing again.
hint: See the 'Note about fast-forwards' in 'git push --help' for details.