错误：

 git pull
error: cannot lock ref 'refs/remotes/origin/master': is at 7c24929668c2c2711b13605b6b0b64f9120ebe9c but expected 5af59c0d0ca1dd073df675f8416b26a19b0a25e4
From github.com:victorcheney/d3demos
 ! 5af59c0..7c24929  master     -> origin/master  (unable to update local ref)

解决方法：

垃圾回收
git remote prune origin // 删除在本地有但在远程库中已经不存在的分支
git pull