C:Usersadmin>npm i webpack@2.1.0 -g  npm ERR! argv "F:\Software\nodejs\node.exe" "F:\Software\nodejs\node_modul es\npm\bin\npm-cli.js" "i" "webpack@2.1.0" "-g" npm ERR! node v4.4.7 npm ERR! npm  v2.15.8  npm ERR! version not found: webpack@2.1.0 npm ERR! npm ERR! If you need help, you may report this error at: npm ERR!     <https://github.com/npm/npm/issues>  npm ERR! Please include the following file with any support request: npm ERR!     C:Usersadmin
pm-debug.log

求问,我想装webpack2.x版本,现在输入 npm i webpack@2.1.0 -g 提示错误,求解?谢谢呀