sudo npm i -g create-react-app
安装了最新的脚手架去新建项目，执行
create-react-app demo
出现下面的错误，，
找不到react-dom最新包》》？？
Installing packages. This might take a couple of minutes.
Installing react, react-dom, and react-scripts...
You appear to be offline.
Falling back to the local Yarn cache.
yarn add v0.27.5
info No lockfile found.
[1/4] Resolving packages...
error Couldn't find any versions for "react-dom" that matches "latest" in our cache. Possible versions: ""
info Visit https://yarnpkg.com/en/docs/cli/add for documentation about this command.
Aborting installation.
yarnpkg add --exact --offline react react-dom react-scripts has failed.