vue-cli 2.x version upgrade to version 3.x
npm install -g @vue/cli
或者
yarn yarn global add @vue/cli
Downgrading from vue-cli 3.x version to version 2.x
npm install -g @vue/cli-init
或者
yarn global add @vue/cli-init
npm install -g @vue/cli
或者
yarn yarn global add @vue/cli
npm install -g @vue/cli-init
或者
yarn global add @vue/cli-init