Unsupported platform for [email protected]: wanted {"os":"linux","arch":"any"}

There is a typo in your command:

npm install copy-webpack-plugin --save dev

Should be:

npm install copy-webpack-plugin --save-dev

(You forgot a dash)

The typo will make npm try to install https://www.npmjs.com/package/dev, which depends on inotify.

Your error message is because inotify only works on Linux and you are on a Mac.