title: Set python version when creating virtualenv using pipenv
body: <p>Using a Raspberry Pi using Debian 4.14.34-v7+, I am trying to get <code>pipenv</code> set up with Python 3.6.5 as the default version of Python. I first install Python 3.6 by compiling it on the Pi (hours...). After making a 'robot' directory, I then install <code>pipenv</code> with <code>sudo pip3 install pipenv</code> and <code>pipenv install --three</code>.</p>
  
  <p>Then I start the shell and open up Python, getting Python 3.5.3&hellip;</p>
  
  
  
  <pre class="lang-none prettyprint-override"><code>pi@raspberrypi:~/robot $ pipenv shell
  Spawning environment shell (/bin/bash). Use 'exit' to leave.
  . /home/pi/.local/share/virtualenvs/robot-XZ3Md9g0/bin/activate
  pi@raspberrypi:~/robot $ . /home/pi/.local/share/virtualenvs/robot-XZ3Md9g0/bin/activate
  (robot-XZ3Md9g0) pi@raspberrypi:~/robot $ python
  Python 3.5.3 (default, Jan 19 2017, 14:11:04) 
  [GCC 6.3.0 20170124] on linux
  Type "help", "copyright", "credits" or "license" for more information.
  &gt;&gt;&gt; exit()
  </code></pre>
  
  <p>I then change the virtualenv by <code>pipenv --python 3.6</code>, but after it correctly (apparently) installs, I immediately get the warning that pipenv still expects Python 3.5&hellip;</p>
  
  <pre class="lang-none prettyprint-override"><code>(robot-XZ3Md9g0) pi@raspberrypi:~/robot $ pipenv --python 3.6
  Virtualenv already exists!
  Remove existing virtualenv? [Y/n]: y
  Removing existing virtualenv…
  Creating a virtualenv for this project…
  Using /usr/local/bin/python3.6m (3.6.5) to create virtualenv…
  ⠋Running virtualenv with interpreter /usr/local/bin/python3.6m
  Using base prefix '/usr/local'
  New python executable in /home/pi/.local/share/virtualenvs/robot-XZ3Md9g0/bin/python3.6m
  Also creating executable in /home/pi/.local/share/virtualenvs/robot-XZ3Md9g0/bin/python
  Installing setuptools, pip, wheel...done.
  
  Virtualenv location: /home/pi/.local/share/virtualenvs/robot-XZ3Md9g0
  Warning: Your Pipfile requires python_version 3.5, but you are using 3.6.5 (/home/pi/.local/share/v/r/bin/python).
    $ pipenv check will surely fail.
  (robot-XZ3Md9g0) pi@raspberrypi:~/robot $ python
  Python 3.6.5 (default, May  3 2018, 11:25:17) 
  [GCC 6.3.0 20170516] on linux
  Type "help", "copyright", "credits" or "license" for more information.
  &gt;&gt;&gt; 
  </code></pre>
  
  <p>How do I set up <code>pipenv</code> to look for Python 3.6, when I first create the virtualenv? I can manually go in and edit the Pipfile, but that seems to be defeating the purpose of having <code>pipenv</code> take care of things for me.</p>