title: how to fix cannot find module graceful-fs error?
body: <p>I have grunt configured and when I run 'grunt serve' I get this error:</p>
  
  <pre><code>Error: Cannot find module 'graceful-fs'
      at Function.Module._resolveFilename (module.js:338:15)
      at Function.Module._load (module.js:280:25)
      at Module.require (module.js:364:17)
      at require (module.js:380:17)
  </code></pre>
  
  <p>how can I fix this error and run my app?</p>