ERROR: While executing gem ... (Gem::FilePermissionError) You don‘t have write permissions for the /Library/Ruby/Gems/2.0.0 directory.
原因是没有写的权限
解决办法
sudo gem install dryrun
执行gem install dryrun错误
原文：http://www.cnblogs.com/krislight1105/p/5204707.html
