yarn add laravel-echo-server
yarn add v1.19.0
[1/4] ? Resolving packages...
[2/4] ? Fetching packages...
error Incorrect integrity when fetching from the cache
info Visit https://yarnpkg.com/en/docs/cli/add for documentation about this command.
解决方法：
1、yarn config set unsafe-disable-integrity-migration false
2、yarn cache clean
3、yarn install -f 或者 直接 yarn add ..
问题解决。