title: npm install npm -g won't update npm to the latest version
body: <p>I am using npm v5.3.0.
  Now I want to update npm to v5.4.1.To do this I type the following in my terminal:</p>
  
  <p><code>npm install -g npm</code></p>
  
  <p>without any errors.However when I type <code>npm -v</code> the version I get is the 5.3.0 not the 5.4.1</p>
  
  <p>I have to mention that I have changed the npm prefix to another directory.
  Any ideas?
  I use Ubuntu 17.04</p>
  
  <p>That's my console output :
  <a href="https://i.stack.imgur.com/9Svbx.png" rel="noreferrer"><img src="https://i.stack.imgur.com/9Svbx.png" alt="enter image description here"></a></p>