title: pip version in Ubuntu is different
body: <p>I meet a issue about pip version in Ubuntu  is different as the following:</p>
  
  <p>This is my virtual machine - Ubuntu 12.04.5 LTS (GNU/Linux 3.11.0-15-generic x86_64)</p>
  
  <p><a href="https://i.stack.imgur.com/E5NwU.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/E5NwU.png" alt="enter image description here"></a></p>
  
  <p>The pip version is 6.0.8 (6.X.X):</p>
  
  <p><a href="https://i.stack.imgur.com/qGzMm.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/qGzMm.png" alt="enter image description here"></a></p>
  
  <p>Another virtual machine is Ubuntu 14.04.3 LTS. It's downloaded form <a href="http://www.ubuntu.com/download/desktop" rel="nofollow noreferrer">Ubuntu  desktop</a>.</p>
  
  <p>The pip version is 1.5.4 (1.X.X):</p>
  
  <p><a href="https://i.stack.imgur.com/bTBgp.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/bTBgp.png" alt="enter image description here"></a></p>
  
  <p>They are in same operation system. Why are they different?</p>