title: Cannot find module 'require-dir' error while running gulp app:serve rails
body: <p>I installed npm, bower and gulp. But while running gulp app:serve, I am getting the following error. 
  Please help me.
  This is the command I run:
  <em>sachin@sachin:~/Desktop/workspace/myproj/angular/ex (master)$gulp app:serve</em></p>
  
  <p>Result I got:</p>
  
  <pre><code>Error: Cannot find module 'require-dir'
      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)
      at Object.&lt;anonymous&gt; (/home/sachin/Desktop/workspace/myproj/angular/ex/gulpfile.js:14:1)
      at Module._compile (module.js:456:26)
      at Object.Module._extensions..js (module.js:474:10)
      at Module.load (module.js:356:32)
      at Function.Module._load (module.js:312:12)
      at Module.require (module.js:364:17)
  </code></pre>