title: usemin define custom step options
body: <p>I have a Gruntfile running concat and uglify with specific options (i.e. mangle toplevel variables) and then I use sed to update the references to the minified files in index.html. This solution works but is not very maintainable because of sed. I was trying to use usemin instead but I could not figure out how to define my own custom steps with the right options for uglifyjs and the doco lacks in examples to do that. I tried to use the same uglify task I had written before:</p>
  
  <pre><code>   uglify: {
        options: {
          banner: '/*! &lt;%= pkg.name %&gt; &lt;%= grunt.template.today("yyyy-mm-dd") %&gt; */\n',
          mangle: {
              except: ['$', 'd3'],
              toplevel: true
          }
        },
        build: {
          src: 'demo/js/&lt;%= pkg.name %&gt;.js',
          dest: 'demo/js/&lt;%= pkg.name %&gt;.min.js'
        }
      },
      useminPrepare : {
          html : 'src/index.html',
          options: {
              flow: {
                  steps: {'js' : ['uglify'] }
              }
          }
      }
  </code></pre>
  
  <p>but I am getting this error:</p>
  
  <p><code>Warning: Cannot find module 'path-to-module\node_modules\grunt-usemin\lib\config\uglify' Use --force to continue.</code></p>
  
  <p>Is it possible to do this and if so, what am i doing wrong here?</p>