title: Vue.js: Invalid options in vue.config.js: "plugins" is not allowed
body: <p>I have a webpack project and I want to use Stylelint for SCSS linting. I have followed the instructions on the Stylelint website and installed:</p>
  
  <pre><code>"stylelint": "^12.0.1",
  "stylelint-webpack-plugin": "^1.1.2",
  </code></pre>
  
  <p>And then I have put this in vue.config.js:</p>
  
  <pre><code>plugins: [
    new StylelintPlugin({
      files: '**/*.s?(a|c)ss'
    })
  ],
  </code></pre>
  
  <p>And when I start the server I get this:</p>
  
  <pre><code>Invalid options in vue.config.js: "plugins" is not allowed
  </code></pre>
  
  <p>I have searched high and low but I have not found anything.
  Any help would be appreciated.</p>
  
  <p>Here is the vue.config.js:</p>
  
  <pre><code>const StylelintPlugin = require('stylelint-webpack-plugin')
  
  module.exports = {
  
    plugins: [
      new StylelintPlugin({
        files: '**/*.s?(a|c)ss'
      })
    ],
  
    assetsDir: 'asset',
  
    configureWebpack: config =&gt; {
      config.entry = '@/wrapper/main.js'
    },
  
    chainWebpack: config =&gt; {
      config.plugins.delete('prefetch')
    },
  
    lintOnSave: undefined,
    runtimeCompiler: true
  }
  </code></pre>