title: grunt-autoprefixer and grunt-postcss not working
body: <p>I have tried both plugins <a href="https://github.com/nDmitry/grunt-autoprefixer" rel="nofollow">grunt-autoprefixer</a> and <a href="https://github.com/nDmitry/grunt-postcss" rel="nofollow">grunt-postcss</a> but neither are adding prefixes. I have tried with something that caniuse.com says requires a prefix (cursor: grab).</p>
  
  <p>Here is my autoprefixer task:</p>
  
  <pre><code>   autoprefixer: {
          dev: {
              no_dest: {
                  src: 'dev/styles.css'
              }
          },
          live: {
              no_dest: {
                  src: 'live/styles.css'
              }
          }
      }
  </code></pre>
  
  <p>And here is my postcss task:</p>
  
  <pre><code>   postcss: {
          dev: {
              options: {
                  processors: [
                      require('autoprefixer-core')({browsers: 'last 1 version'}).postcss
                  ]
              },
              dist: {
                  src: 'dev/styles.css'
              }
          }
      }
  </code></pre>