title: Generating sourcemaps with npm scripts using node-sass and postcss autoprefixer
body: <p>Is it possible to generate fully working sourcemaps using node-sass and postcss autoprefixer when piping output from one to another? I currently have the following in package.json:</p>
  
  <pre><code>"scripts": {
      "sass": "node-sass sass/app.scss --source-map true --source-map-embed true",
      "postcss:autoprefixer": "postcss --use autoprefixer -b 'last 2 versions' --map",
      "css": "npm run sass -s | npm run postcss:autoprefixer -s &gt; css/app.css"
  }
  </code></pre>
  
  <p>This produces a semi-working inline sourcemap, but the links to original files are incorrect, so clicking on them in Chrome devtools won't load them (it seems like they are processed as relative links and then referenced from the css folder). I tried to fix this by adding the <code>--source-map-contents true</code> option to node-sass, but then autoprefixer bugs out, I suspect because it doesn't like the line length of the dataUri.</p>
  
  <p>Ideally I'd prefer to output a separate .map file anyway, but setting the node-sass option to <code>--source-map css/app.css.map</code> doesn't write anything out, presumably because only the css is output to stdout.</p>