在終端安裝任何包，執行 npm i均報錯
npm ERR! code ENOTFOUND
npm ERR! errno ENOTFOUND
npm ERR! network request to https://registry.npmjs.org/ultron/-/ultron-1.1.1.tgz failed, reason: getaddrinfo ENOTFOUND registry.npmjs.org
npm ERR! network This is a problem related to network connectivity.
npm ERR! network In most cases you are behind a proxy or have bad network settings.
npm ERR! network
npm ERR! network If you are behind a proxy, please make sure that the
npm ERR! network 'proxy' config is set properly. See: 'npm help config'
npm 代理出錯
可嘗試依次執行：
npm config get proxy
npm config get https-proxy
兩者均返回null，否則，執行set null的命令，再安裝淘寶鏡像
npm config set registry http://registry.cnpmjs.org/
npm install -g cnpm --registry=https://registry.npm.taobao.org
之后可以執行npm i
了解不多，原理方面不太清楚，歡迎多多指教