nodejs fs: re-evaluating native

node6.x版本中npm安装fs-extra时，发生以下错误：

(node:4605) fs: re-evaluating native module sources is not supported. If you are using the graceful-fs module, please update it to a more recent version.

参考链接：
http://stackoverflow.com/questions/37346512/how-to-fix-fs-re-evaluating-native-module-sources-is-not-supported-graceful
建议安装：graceful-fs@4.1.4
但是最近用了下node6，有点小坑，还是切回5了。等等再升级吧。