title: npm -v reports error when node.js has been installed
body: <p>I install node.js on centos6.5 and node.js has no problem ,but when i test npm -v</p>
  
  <pre><code>[root@localhost ~]# npm -v
  
  module.js:340
      throw err;
            ^
  Error: Cannot find module 'npmlog'
      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 /usr/bin/npm:18:11
      at Object.&lt;anonymous&gt; (/usr/bin/npm:86:3)
      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)
  </code></pre>