title: Vue3 autoprefixer config issue
body: <p>I have a new project that was created with Vue-cli 3 using <code>vue create my-new-project</code>. I am using CSS grid for some layout things and i need to support IE11 and newer. Vue docs say that autoprefixer is loaded and enabled by default but its not working. I cant get it to work in either npm run build or npm run serve. Works fine in chrome but IE11 its not working. Im sure there is some config that needs to be done but im unsure what that may be.</p>
  
  <p>.browserslistrc:</p>
  
  <pre><code>&gt; 1%
  last 4 versions
  </code></pre>
  
  <p>postcss.config.js:</p>
  
  <pre><code>module.exports = {
    plugins: {
      autoprefixer: {}
    }
  };
  </code></pre>