title: cannot install django 2.0.6 using pipenv
body: <p>following the author's step, saw this command<br> <code>$ pipenv install django==2.0.6</code> <br> in a book <strong>Django for beginners</strong> it seems to have been working for the author but when I try to execute it on the terminal it gives me following error.</p>
  
  <pre><code>    sysadmin@R902R6HD:~/Desktop/helloworld$ pipenv install django=2.0.6
  /usr/local/lib/python2.7/dist-packages/pipenv/vendor/requests/__init__.py:83: RequestsDependencyWarning: Old version of cryptography ([1, 2, 3]) may cause slowdown.
    warnings.warn(warning, RequestsDependencyWarning)
  Installing django=2.0.6...
  ⠋WARNING: Invalid requirement, parse error at "u'=2.0.6'"
  ABORTING INSTALL... You will have to reinstall any packages that failed to install.
  You may have to manually run pipenv lock when you are finished.
  /usr/local/lib/python2.7/dist-packages/pipenv/_compat.py:113: ResourceWarning: Implicitly cleaning up &lt;TemporaryDirectory '/tmp/pipenv-67QFfh-requirements'&gt;
    warnings.warn(warn_message, ResourceWarning)
  sysadmin@R902R6HD:~/Desktop/helloworld$ pipenv install django==2.0.6
  /usr/local/lib/python2.7/dist-packages/pipenv/vendor/requests/__init__.py:83: RequestsDependencyWarning: Old version of cryptography ([1, 2, 3]) may cause slowdown.
    warnings.warn(warning, RequestsDependencyWarning)
  Installing django==2.0.6...
  Collecting django==2.0.6
  
  Error:  An error occurred while installing django==2.0.6!
    Could not find a version that satisfies the requirement django==2.0.6 (from versions: 1.1.3, 1.1.4, 1.2, 1.2.1, 1.2.2, 1.2.3, 1.2.4, 1.2.5, 1.2.6, 1.2.7, 1.3, 1.3.1, 1.3.2, 1.3.3, 1.3.4, 1.3.5, 1.3.6, 1.3.7, 1.4, 1.4.1, 1.4.2, 1.4.3, 1.4.4, 1.4.5, 1.4.6, 1.4.7, 1.4.8, 1.4.9, 1.4.10, 1.4.11, 1.4.12, 1.4.13, 1.4.14, 1.4.15, 1.4.16, 1.4.17, 1.4.18, 1.4.19, 1.4.20, 1.4.21, 1.4.22, 1.5, 1.5.1, 1.5.2, 1.5.3, 1.5.4, 1.5.5, 1.5.6, 1.5.7, 1.5.8, 1.5.9, 1.5.10, 1.5.11, 1.5.12, 1.6, 1.6.1, 1.6.2, 1.6.3, 1.6.4, 1.6.5, 1.6.6, 1.6.7, 1.6.8, 1.6.9, 1.6.10, 1.6.11, 1.7, 1.7.1, 1.7.2, 1.7.3, 1.7.4, 1.7.5, 1.7.6, 1.7.7, 1.7.8, 1.7.9, 1.7.10, 1.7.11, 1.8a1, 1.8b1, 1.8b2, 1.8rc1, 1.8, 1.8.1, 1.8.2, 1.8.3, 1.8.4, 1.8.5, 1.8.6, 1.8.7, 1.8.8, 1.8.9, 1.8.10, 1.8.11, 1.8.12, 1.8.13, 1.8.14, 1.8.15, 1.8.16, 1.8.17, 1.8.18, 1.8.19, 1.9a1, 1.9b1, 1.9rc1, 1.9rc2, 1.9, 1.9.1, 1.9.2, 1.9.3, 1.9.4, 1.9.5, 1.9.6, 1.9.7, 1.9.8, 1.9.9, 1.9.10, 1.9.11, 1.9.12, 1.9.13, 1.10a1, 1.10b1, 1.10rc1, 1.10, 1.10.1, 1.10.2, 1.10.3, 1.10.4, 1.10.5, 1.10.6, 1.10.7, 1.10.8, 1.11a1, 1.11b1, 1.11rc1, 1.11, 1.11.1, 1.11.2, 1.11.3, 1.11.4, 1.11.5, 1.11.6, 1.11.7, 1.11.8, 1.11.9, 1.11.10, 1.11.11, 1.11.12, 1.11.13, 1.11.14)
  No matching distribution found for django==2.0.6 
  </code></pre>