docs: remove mention of Node.js v8 npm workaround, as it's been fixed [skip ci]

Author: haoqunjiang

docs/guide/installation.md

@@ -7,9 +7,6 @@ If you have the previous `vue-cli` (1.x or 2.x) package installed globally, you
 
 ::: tip Node Version Requirement
 Vue CLI 4.x requires [Node.js](https://nodejs.org/) version 8.9 or above (v10+ recommended). You can manage multiple versions of Node on the same machine with [n](https://github.com/tj/n), [nvm](https://github.com/creationix/nvm) or [nvm-windows](https://github.com/coreybutler/nvm-windows).
-
-As Node.js v8 has reached end-of-life, it's now recommended to use Node.js v10+ for best compatibility.
-If you have to stay with Node.js v8, please make sure npm v6 is used as the default package manager. (`npm -v` to check the version, and `vue config --set packageManager npm` to set the default package manager.)
 :::
 
 To install the new package, use one of the following commands. You need administrator privileges to execute these unless npm was installed on your system through a Node.js version manager (e.g. n or nvm).

docs/zh/guide/installation.md

@@ -7,9 +7,6 @@ Vue CLI 的包名称由 `vue-cli` 改成了 `@vue/cli`。
 
 ::: tip Node 版本要求
 Vue CLI 4.x 需要 [Node.js](https://nodejs.org/) v8.9 或更高版本 (推荐 v10 以上)。你可以使用 [n](https://github.com/tj/n)，[nvm](https://github.com/creationix/nvm) 或 [nvm-windows](https://github.com/coreybutler/nvm-windows) 在同一台电脑中管理多个 Node 版本。
-
-由于 Node.js v8 已不再维护，我们建议使用 Node.js v10 以上的版本，以保证最佳的兼容性。
-如果暂时无法升级 Node.js 版本，请使用 npm v6 作为默认的包管理工具。（可以用 `npm -v` 检查 npm 版本，然后运行 `vue config --set packageManager npm` 以设置默认包管理工具。）
 :::
 
 可以使用下列任一命令安装这个新的包：