title: Pipenv: Specify version of setuptools
body: <p>I'm running into an error with <code>setuptools</code> that is supposedly fixed in version <code>31.0.0</code>.  I'm using <code>pipenv</code> as a virtual environment manager, so I have both a <code>Pipfile</code> and <code>Pipfile.lock</code>.</p>
  
  <p>I've specified:</p>
  
  <pre><code>setuptools = "==31.0.0"
  </code></pre>
  
  <p>in my <code>Pipfile</code></p>
  
  <p>I run <code>pipenv install</code> but don't see anything show up in my <code>Pipfile.lock</code>.  However, if I run:</p>
  
  <p><code>pipenv run
  import setuptools
  setuptools.__version__</code></p>
  
  <p>I get back: </p>
  
  <p><code>40.0.0</code></p>
  
  <p>Any idea how I can specify <code>31.0.0</code> and why my current approach is incorrect?</p>
  
  <p>Thanks!</p>