我有2个分支，master＆amp; secondary并通过合并master => secondary.
有一次，master有几个被删除的子模块，并且重新添加了相同的子模块。
我现在正尝试将master合并到secondary但是每当我尝试从master切换到secondary时，我都会在子模块上收到这些错误消息重写：
warning: unable to rmdir libs/AFNetworking: Directory not empty
warning: unable to rmdir libs/MBProgressHUD: Directory not empty
Branch secondary set up to track remote branch secondary from origin.
Switched to a new branch 'secondary'
'master'分支就像这样开始：
git clone repourl:master.git
cd project_directory
git submodule update --init <= in master at the moment
git checkout secondary