npm安装cnpm，解决node12\14安装cnpm失败问题

cnpm 仓库 https://www.npmjs.com/package/cnpm?activeTab=readme
cnpm源码：http://github.com/cnpm/cnpm

新版的cnpm不支持版本<=14的node,因此,12\14这些低版本的要加上@7.1.1

node>14

npm install cnpm -g --registry=https://registry.npmmirror.com

node<=14

npm install cnpm@7.1.1 -g --registry=https://registry.npmmirror.com

卸载

npm uninstall -g cnpm