git上传项目error: failed to push some refs to 'https://git.oschina.net/xxxxxx/aaaaaa.git'

git push -u origin master

To https://git.oschina.net/xxxxxx/aaaaaa.git ! [rejected]        master -> master (fetch first)
error: failed to push some refs to 'https://git.oschina.net/xxxxxx/aaaaaa.git'
hint: Updates were rejected because the remote contains work that you do
hint: not have locally. This is usually caused by another repository pushing
hint: to the same ref. You may want to first integrate the remote changes
hint: (e.g., 'git pull ...') before pushing again.
hint: See the 'Note about fast-forwards' in 'git push --help' for details.

git push -f origin master

Counting objects: 3, done.
Writing objects: 100% (3/3), 228 bytes | 0 bytes/s, done.
Total 3 (delta 0), reused 0 (delta 0)
To https://git.oschina.net/xxxxxx/aaaaaa.git + 35f6844...8b04c7b master -> master (forced update)