问题描述(Issue)
it throws “Cannot find module ‘./lib’” when I run “npm install -g xxx” command.
Mac升级到node 5.0之后，执行npm install命令出现Cannot find module ‘./lib’的错误。
问题原因（Cause）
The current theory is that a change made to the OS X installer for Node is causing two npm installations to be overlaid, which is understandably causing problems.
解决办法（Solution）
If you remove /usr/local/lib/node_modules/npm and rerun the Node 5.0 installer, you should be left with a working npm.
移除 /usr/local/lib/node_modules/npm目录，重装node 5.0.