title: Cannot import six.python_2_unicode_compatible in Django application
body: <p>Due a new requirement on my Django app, I started using zeep. I installed it as usual throught an existing virtualenv.
  The problem is that, when i tried to deploy my app, using Apache and mod_wsgi, it doesn't work, returning the following error:</p>
  
  <pre><code>ImportError at /prwn/
  cannot import name python_2_unicode_compatible
  
  /home/prwn/env/lib/python2.7/site-packages/zeep/wsdl/definitions.py in &lt;module&gt;
  from six import python_2_unicode_compatible 
  </code></pre>
  
  <p>The weirdest thing is that when my app is ran using runserver and the same virtualenv, it runs fine.
  I tried creating a new virtualenv, a new Apache's virtualhost, even changing the permisions to 777 to the whole virtualenv,
  and still not working.</p>
  
  <p>I use the versions <strong>0.23.0 of zeep</strong>, <strong>1.10.0 of six</strong> and <strong>python 2.7</strong></p>