title: npm git repository not updating versions
body: <p>I have an git repo and I'm trying to set it as a dependency in my project.
  Using NPM, my <code>package.json</code> looks like this:</p>
  
  <pre><code>"devDependencies": {
    "grunt": "~0.4.0",
    "grunt-contrib-connect": "~0.2.0",
    "grunt-contrib-watch": "~0.3.1",
    "custom":     "git://github.com/myGitHubRepo/repo.js.git#b7d53a0cfbe496ad89bde6f22324219d098dedb3",
    "grunt-contrib-copy": "~0.4.0"
  }
  </code></pre>
  
  <p>On the first</p>
  
  <pre><code>npm install
  </code></pre>
  
  <p>It install everything and fetches the repository with no problem. But if I change this commit hash to let's say</p>
  
  <pre><code>"custom":     "git://github.com/myGitHubRepo/repo.js.git#d6da3a0...", // a different one
  </code></pre>
  
  <p>It doesn't update! Can anyone point me out how could I get this behavior?</p>
  
  <p>I would simply like to share this code and be able to at some point change this version and the <code>npm</code> would automatically update this.</p>