PurgeCSS fails with NuxtJS example

Describe the bug I copied the relevant part from your example, but when I try to run nuxt build, It throws an error: Cannot read property 'compilation' of undefined. It comes from purgecss-webpack-plugin.js:141:27

To Reproduce Steps to reproduce the behavior:

1. I used the following nuxt.config.js

const PurgecssPlugin = require('purgecss-webpack-plugin');
const glob = require('glob-all');
const path = require('path');

module.exports = {
  generate: {
    fallback: true,
  },
  /*
  ** Headers of the page
  */
  head: {
    title: 'nuxt-test',
    meta: [
      { charset: 'utf-8' },
      { name: 'viewport', content: 'width=device-width, initial-scale=1' },
      { hid: 'description', name: 'description', content: 'Nuxt.js project' }
    ],
    link: [
      { rel: 'icon', type: 'image/x-icon', href: '/favicon.ico?v2' },
    ]
  },
  /*
  ** Customize the progress bar color
  */
  loading: { color: '#3B8070' },
  /*
  ** Build configuration
  */
  build: {
    extractCSS: true,
    /*
    ** Run ESLint on save
    */
    extend (config, { isDev, isClient }) {
      if (isDev && isClient) {
        config.module.rules.push({
          enforce: 'pre',
          test: /\.(js|vue)$/,
          loader: 'eslint-loader',
          exclude: /(node_modules)/
        })
      }
      if (!isDev) {
        // Remove unused CSS using purgecss. See https://github.com/FullHuman/purgecss
        // for more information about purgecss.
        config.plugins.push(
          new PurgecssPlugin({
            paths: glob.sync([
              path.join(__dirname, './pages/**/*.vue'),
              path.join(__dirname, './layouts/**/*.vue'),
              path.join(__dirname, './components/**/*.vue')
            ]),
            whitelist: ['html', 'body']
          })
        )
      }
    },
  }
}

1. I run npm run build from terminal.

Expected behavior I expect the build to run succesfully with my unused css purged.

Screenshots

Desktop (please complete the following information):

• OS: Ubuntu 16.04
• Version of Purgecss: “purgecss-webpack-plugin”: “^1.1.0” // insatlled from npm
• Webpack version: 3.12.0 // came with NuxtJS

Additional context If I remove the PurgeCSS plugin, the build runs succefully

[jsnanigans]

In the new version 1.2.0 webpack V3 and V4 are supported, so you can use the normal release now to also get the newest purgecss features

[jsnanigans]

@Ffloriel I think there is no need to update the instructions, this evening I would like to update the purgecss-webpack-plugin to work with both webpack v3 and v4 so the example will work again