title: CSS Loader has been initialised using an options object that does not match the API schema
body: <p>Production build fails with the following error:</p>
  
  <pre><code>ValidationError: Invalid options object. CSS Loader has been initialised using an options object that does not match the API schema.
   - options has an unknown property 'minimize'. These properties are valid:
     object { url?, import?, modules?, sourceMap?, importLoaders?, localsConvention?, onlyLocals? }
      at validate (/Users/username/Sites/projectname/node_modules/css-loader/node_modules/schema-utils/dist/validate.js:85:11)
      at Object.loader (/Users/username/Sites/projectname/node_modules/css-loader/dist/index.js:34:28)
  </code></pre>
  
  <p>Using this webpack template: <a href="http://vuejs-templates.github.io/webpack/" rel="noreferrer">http://vuejs-templates.github.io/webpack/</a>, updated to Webpack 4 and faced build issues, package.json:</p>
  
  <pre><code>{
    "name": "projectname",
    "private": true,
    "scripts": {
      "dev": "webpack-dev-server --inline --progress --config webpack.config.js --port 3000 --hot",
      "start": "npm run dev",
      "build": "cross-env NODE_ENV=production webpack --progress --hide-modules"
    },
    "dependencies": {
      "@vue/cli-service": "^3.2.0",
      "axios": "^0.18.0",
      "babel-polyfill": "^6.26.0",
      "cross-env": "^5.2.0",
      "css-loader": "^3.2.1",
      "jquery": "^3.3.1",
      "moment": "^2.22.2",
      "style-loader": "^1.0.1",
      "swiper": "^4.5.0",
      "v-tabs-router": "^1.4.0",
      "vee-validate": "^2.1.0-beta.9",
      "vue": "^2.5.2",
      "vue-awesome-swiper": "^3.1.3",
      "vue-backtotop": "^1.6.1",
      "vue-carousel": "^0.18.0",
      "vue-cleave-component": "^2.1.2",
      "vue-instant": "^1.0.2",
      "vue-jsonp": "^0.1.8",
      "vue-magic-line": "^0.2.1",
      "vue-masked-input": "^0.5.2",
      "vue-resource": "^1.5.1",
      "vue-router": "^3.0.2",
      "vue-select": "^2.5.1",
      "vue-slider-component": "^2.8.0",
      "vue-smooth-scroll": "^1.0.13",
      "vuejs-datepicker": "^1.5.3",
      "vuelidate": "^0.7.4",
      "vuex": "^3.0.1"
    },
    "devDependencies": {
      "autoprefixer": "^7.1.2",
      "babel-core": "^6.22.1",
      "babel-helper-vue-jsx-merge-props": "^2.0.3",
      "babel-loader": "^7.1.1",
      "babel-plugin-syntax-jsx": "^6.18.0",
      "babel-plugin-transform-runtime": "^6.22.0",
      "babel-plugin-transform-vue-jsx": "^3.5.0",
      "babel-preset-env": "^1.3.2",
      "babel-preset-stage-2": "^6.22.0",
      "chalk": "^2.0.1",
      "copy-webpack-plugin": "^4.0.1",
      "extract-text-webpack-plugin": "^3.0.0",
      "file-loader": "^5.0.2",
      "friendly-errors-webpack-plugin": "^1.6.1",
      "html-webpack-plugin": "^3.2.0",
      "node-notifier": "^5.1.2",
      "node-sass": "^4.13.0",
      "optimize-css-assets-webpack-plugin": "^5.0.3",
      "ora": "^1.2.0",
      "portfinder": "^1.0.13",
      "postcss-import": "^12.0.1",
      "postcss-loader": "^3.0.0",
      "postcss-url": "^8.0.0",
      "rimraf": "^2.6.0",
      "sass-loader": "^8.0.0",
      "semver": "^5.3.0",
      "shelljs": "^0.7.6",
      "uglifyjs-webpack-plugin": "^1.1.1",
      "url-loader": "^1.1.2",
      "vue-loader": "^14.2.2",
      "vue-resource": "^1.5.1",
      "vue-style-loader": "^4.1.2",
      "vue-template-compiler": "^2.5.2",
      "webpack": "^4.41.2",
      "webpack-cli": "^3.3.10",
      "webpack-dev-server": "^3.9.0"
    },
    "engines": {
      "node": "&gt;= 6.0.0",
      "npm": "&gt;= 3.0.0"
    },
    "browserslist": [
      "&gt; 1%",
      "last 2 versions",
      "not ie &lt;= 8"
    ]
  }
  </code></pre>
  
  <p>I've checked with <code>grep -rl 'minimize' .</code> in a project root, but didn't found any related options. Wth..</p>