title: 'grunt' command doesn't do anything
body: <p>I'm following the grunt <a href="http://gruntjs.com/getting-started">getting started guide</a> for my new app, but I'm having some trouble.</p>
  
  <p>This is my Gruntfile.js</p>
  
  <pre><code>module.exports = function(grunt) {
  
    // Project configuration.
    grunt.initConfig({
      pkg: grunt.file.readJSON('package.json'),
      uglify: {,
        build: {
          src: 'js/*.js',
          dest: 'build/*.min.js'
        }
      }
    });
  
    // Load the plugin that provides the "uglify" task.
    grunt.loadNpmTasks('grunt-contrib-uglify');
  
    // Default task(s).
    grunt.registerTask('default', ['uglify']);
  
  };
  </code></pre>
  
  <p>This is my package.json</p>
  
  <pre><code>{
    "name": "My App",
    "version": "0.0.0",
    "description": "",
    "author": "",
    "license": "N/A",
    "devDependencies": {
      "grunt": "~0.4.2",
      "grunt-contrib-jshint": "~0.8.0",
      "grunt-contrib-uglify": "~0.2.7"
    }
  }
  </code></pre>
  
  <p>I have the grunt-cli package installed and I've run npm install to get a local version of grunt and the contrib libraries.</p>
  
  <p>But when I run either <code>grunt</code> or <code>grunt uglify</code> nothing happens.</p>
  
  <pre><code>$ grunt
  $ grunt uglify
  $
  </code></pre>
  
  <p>Any idea what I have missed or what could cause this behaviour?</p>
  
  <p>EDIT: I just installed mocha too and I get the same issue with that: no output. Maybe there is a problem with my node or npm installation</p>