操作git从远端拉去代码时，报出了下面的问题，cannot lock ref，
git -c diff.mnemonicprefix=false -c core.quotepath=false -c credential.helper=sourcetree fetch origin
error: cannot lock ref 'refs/remotes/origin/dev': ref refs/remotes/origin/dev is at 19070aed6873f8d58f35e4631272b59f13927a1c but expected 8a5b3bda0778070bd6b92123556475c9484e04b8
From 120.26.77.241:dongjia/php
! 8a5b3bd..007af81 dev -> origin/dev (unable to update local ref)
Completed with errors, see above
From 120.26.77.241:yourWorkspace/yourProject
遇到了两种解决方法，
切到项目根目录，
方法一 ： 执行git remote prune origin，让后git fetch；（推荐使用）
方法二： 执行rm .git/refs/remotes/origin/dev(develop)，然后git fetch；使用此方法需要权限
