npm 更新至最新版本

有时npm版本低了，一些操作有问题，要更新成最新。

官网中：  https://www.npmjs.com/get-npm     先查看对应的 node 版本 和 npm版本

Check that you have node and npm installed

To check if you have Node.js installed, run this command in your terminal:

node -v

To confirm that you have npm installed you can run this command in your terminal:

npm -v

npm versions

npm is a separate project from Node.js, and tends to update more frequently. As a result, even if you’ve just downloaded Node.js (and therefore npm), you’ll probably need to update your npm. Luckily, npm knows how to update itself! To update your npm, type this into your terminal:

npm install npm@latest -g

更新到npm 最新版本