[rejected] master -> master (fetch first)(non-fast forward)

git push 时候遇到的错误：

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.

错误原因：

两个不同的项目需要先合并。

解决办法：

git pull origin master –allow-unrelated-histories