title: Grunt Usemin: How to define targets?
body: <p>I was wondering how i can use "targets" with grunt usemin. <br >
  e.g. to run sth. like: <strong>grunt usemin:app</strong></p>
  
  <p>This is what I tried (Error: Warning: Object # has no method 'indexOf' Use --force to continue.) – same for useminPrepare</p>
  
  <pre><code>   usemin: {
          app : {
              html: ['&lt;%= config.app.dist %&gt;/app/{,*/}*.html'],
              css: ['&lt;%= config.app.dist %&gt;/app/css/{,*/}*.css'],
              options: {
                  dirs: ['&lt;%= config.app.dist %&gt;/app']
              }
          },
          site: {
              html: ['&lt;%= config.site.dist %&gt;/{,*/}*.html'],
              css: ['&lt;%= config.site.dist %&gt;/css/{,*/}*.css'],
              options: {
                  dirs: ['&lt;%= config.site.dist %&gt;']
              }
          }
      },
  </code></pre>