エラーログ
$ vue add vuetify
WARN There are uncommitted changes in the current repository, it's recommended to commit or stash them first.
? Still proceed? Yes
📦 Installing vue-cli-plugin-vuetify...
yarn add v1.22.17
[1/4] 🔍 Resolving packages...
[2/4] 🚚 Fetching packages...
[3/4] 🔗 Linking dependencies...
[4/4] 🔨 Building fresh packages...
success Saved lockfile.
success Saved 1 new dependency.
info Direct dependencies
└─ vue-cli-plugin-vuetify@2.4.5
info All dependencies
└─ vue-cli-plugin-vuetify@2.4.5
✨ Done in 3.94s.
✔ Successfully installed plugin: vue-cli-plugin-vuetify
? Choose a preset: Default (recommended)
🚀 Invoking generator for vue-cli-plugin-vuetify...
ERROR Error: Line 15: Unexpected token ...
Error: Line 15: Unexpected token ...
at ErrorHandler.constructError (/Users/~~~/.config/yarn/global/node_modules/esprima/dist/esprima.js:5012:22)
at ErrorHandler.createError (/Users/~~~/.config/yarn/global/node_modules/esprima/dist/esprima.js:5028:27)
at Parser.unexpectedTokenError (/Users/~~~/.config/yarn/global/node_modules/esprima/dist/esprima.js:1985:39)
at Parser.throwUnexpectedToken (/Users/~~~/.config/yarn/global/node_modules/esprima/dist/esprima.js:1995:21)
at Parser.parseObjectPropertyKey (/Users/~~~/.config/yarn/global/node_modules/esprima/dist/esprima.js:2499:33)
at Parser.parseObjectProperty (/Users/~~~/.config/yarn/global/node_modules/esprima/dist/esprima.js:2534:25)
at Parser.parseObjectInitializer (/Users/~~~/.config/yarn/global/node_modules/esprima/dist/esprima.js:2602:35)
at Parser.inheritCoverGrammar (/Users/~~~/.config/yarn/global/node_modules/esprima/dist/esprima.js:2285:37)
at Parser.parsePrimaryExpression (/Users/~~~/.config/yarn/global/node_modules/esprima/dist/esprima.js:2354:38)
at Parser.inheritCoverGrammar (/Users/~~~/.config/yarn/global/node_modules/esprima/dist/esprima.js:2285:37)
解決策
事前に作ってしまっていたvue.config.jsファイルを削除してから再度vue add vuetifyを実行する。
（削除ではなく中身を空にするだけでも良いかも）