title: Autoprefix loader breaks scss compilation in Webpack
body: <p>I'm unable to get <a href="https://github.com/passy/autoprefixer-loader" rel="nofollow">autoprefixer-loader</a> 1.10 to prefix my scss/css (apparently 1.20 is broken). After adding the loader, it no longer compiles mixins properly. When I remove the errored mixins, it compiles, but doesn't prefix. Here's Webpack's compilation details from terminal, and my module structure. Any help would be appreciated.</p>
  
  <p><a href="https://gist.github.com/zachshallbetter/efafbffa7e08bcc0aab4" rel="nofollow">https://gist.github.com/zachshallbetter/efafbffa7e08bcc0aab4</a></p>
  
  <pre><code>  module: {
      loaders: [{
        test: /\.jsx?$/,
        loaders: ['react-hot', 'babel'],
        include: path.join(__dirname, 'app/scripts')
      },
      {
        test: /\.scss$|\.css$/,
        loader: 'style-loader!css-loader!sass-loader'
      },
      {
        test: /\.jpe?g$|\.gif$|\.png$|\.svg$|\.woff$|\.ttf$|\.wav$|\.mp3$/,
        loader: "file"
      },
      {
        test: /\.json$/,
        loader: "raw-loader"
      }]
    }
  </code></pre>