title: Can't get Sass Source Maps working with grunt-autoprefixer
body: <p>I'm using Grunt 0.4.5 with these dependencies in my project:</p>
  
  <pre><code>"grunt": "~0.4.5",
  "grunt-contrib-concat": "~0.5.0",
  "grunt-contrib-uglify": "~0.6.0",
  "grunt-contrib-watch": "~0.6.1",
  "grunt-contrib-sass": "~0.8.1"
  </code></pre>
  
  <p>I've just noticed that <a href="https://github.com/nDmitry/grunt-autoprefixer" rel="nofollow">grunt-autoprefixer</a> didn't get added to my package.json file. Is that because it doesn't have the grunt-contrib prefix? Anyway, Source Maps work for me when I remove autoprefixer from my watch task, but as soon as I add it in again the comment at the very end of the compiled css file gets removed. </p>
  
  <p>This is my autoprefixer config:</p>
  
  <pre><code>    autoprefixer: {
          options: {
              browsers: ['last 2 version', 'ie 8', 'ie 9']
          },
          single_file: {
                options: {
                  // Target-specific options go here.
                },
                src: 'library/css/style.css',
                dest: 'library/css/style.css'
              },
          sourcemap: {
              options: {
                  map: true
              }
          },
      },
  </code></pre>
  
  <p>My Sass config looks like this:</p>
  
  <pre><code>    sass: {
          dist: {
              options: {
                  style: 'expanded',
                  debugInfo: true,
                  sourcemap: true
              },
              files: {
                  'library/css/style.css': 'library/scss/style.scss'
              }
          } 
      },
  </code></pre>
  
  <p>and here's my watch task:</p>
  
  <pre><code>    watch: {
          options: {
              livereload: true,
              },
          scripts: {
              files: ['library/js/*.js'],
              tasks: ['concat', 'uglify'],
              options: {
                  spawn: false,
              },
          },
          css: {
              files: ['library/scss/*.scss'],
              tasks: ['sass', 'autoprefixer'],
              sourceComments: 'normal',
              options: {
                  spawn: false,
              }
          },
          page: {
              files: ['*.php', '*.html']
          }
      }
  </code></pre>
  
  <p>I don't get why autoprefixer has to interfere with the source map at all to be honest, I tried using <code>false</code> instead of true, specifying the sourcemap manually as per the example in the grunt-autoprefixer repo, but whatever I do the comment - <code>/*# sourceMappingURL=style.css.map */</code> gets stripped from the file and source maps don't work in chrome.</p>
  
  <p>EDIT: Sorry, I just got it to work by using:</p>
  
  <pre><code>        sourcemap: {
              options: {
                  map: true
              },
              src: 'library/css/style.css',
              dest: 'library/css/style.css' // -&gt; dest/css/file.css, dest/css/file.css.map
          },
  </code></pre>
  
  <p>I'd be interested to know, for performance reasons, do I need to bother specifying a sourcemap option at all in the <code>grunt-contrib-sass</code> config now? It takes me about 2.4s to compile so every 0.1s counts!</p>