npm升级自身

参考：https://github.com/felixrieseberg/npm-windows-upgrade

Usage

First, ensure that you can execute scripts on your system by running the following command from an elevated PowerShell. To run PowerShell as Administrator, click Start, search for PowerShell, right-click PowerShell and select Run as Administrator.

Set-ExecutionPolicy Unrestricted -Scope CurrentUser -Force

Then, to install and use this upgrader tool, run (also from an elevated PowerShell or cmd.exe):

npm install --global --production npm-windows-upgrade
npm-windows-upgrade

Want to just install the latest version? Sure:

npm-windows-upgrade --npm-version latest

The tool will show you a list of all the published and available versions of npm (including pre-release and beta versions). Choose the one you want to install and let it do its thing!