title: Error generating source map - grunt and sass configuration
body: <p>I am trying to use sass with grunt. I have installed ruby, sass and grunt in my path.<br>
  The versions are,  </p>
  
  <blockquote>
    <p>node: 0.10.20<br>
      npm: 1.3.11<br>
      grunt-cli:  0.1.13<br>
      grunt: 0.4.5<br>
      sass: 3.4.4</p>
  </blockquote>
  
  <p>my package json is,</p>
  
  <pre><code>"private": true,
  "devDependencies": {
      "express": "4.x",
      "grunt": "~0.4.1",
      "grunt-contrib-sass": "~0.3.0",
      "grunt-contrib-watch": "~0.4.4" 
  }
  </code></pre>
  
  <p>my grunt file is,</p>
  
  <pre><code>module.exports = function(grunt) {
      grunt.initConfig({
          pkg: grunt.file.readJSON('package.json'),
          sass: {
              dist: {
                  files: {
                      'style/style.css' : 'sass/home.scss'
                  }
              }
          },
          watch: {
              css: {
                  files: '**/*.scss',
                  tasks: ['sass']
              }
          }
      });
      grunt.loadNpmTasks('grunt-contrib-sass');
      grunt.loadNpmTasks('grunt-contrib-watch');
      grunt.registerTask('default',['watch']);
  }
  </code></pre>
  
  <p>Now if i tried "grunt" command, i am getting the below error. Any help?</p>
  
  <p><strong>run: grunt or grunt watch or grunt sass</strong></p>
  
  <p><strong>error:</strong></p>
  
  <pre><code>Running "sass:dist" (sass) task
  Error: Error generating source map: couldn't determine public URL for the source
   stylesheet.
           No filename is available so there's nothing for the source map to link
  to.
          on line  of standard input
    Use --trace for backtrace.
  Warning: Error: Error generating source map: couldn't determine public URL for t
  he source stylesheet.
           No filename is available so there's nothing for the source map to link
  to.
          on line  of standard input
    Use --trace for backtrace. Use --force to continue.
  
  Aborted due to warnings.
  </code></pre>
  
  <p>any idea?</p>