title: Pipenv failing to install any packages
body: <p>I'm trying to make a virtual environment for a script of mine using pipenv, but whenever I try to install any package I get the following error message:</p>
  
  <pre><code>"Command "python setup.py egg_info" failed with error code 1"
  </code></pre>
  
  <p>For example, when I try to install pandas:</p>
  
  <pre><code>mycomputer-admin$ pipenv install pandas
  Installing pandas...
  Collecting pandas
    Using cached https://files.pythonhosted.org/packages/d8/ba/d2c6578afca709e211ac1cd836a66a6a042f1a773a970be345d9d08be426/pandas-0.23.3-cp36-cp36m-macosx_10_6_intel.macosx_10_9_intel.macosx_10_9_x86_64.macosx_10_10_intel.macosx_10_10_x86_64.whl
  Collecting numpy&gt;=1.9.0 (from pandas)
    Using cached https://files.pythonhosted.org/packages/6a/d5/218414f0f41cb3f183d55d68dbcd996fa3602d5849bdf2ad6c059e98fa68/numpy-1.15.0-cp36-cp36m-macosx_10_6_intel.macosx_10_9_intel.macosx_10_9_x86_64.macosx_10_10_intel.macosx_10_10_x86_64.whl
  Collecting python-dateutil&gt;=2.5.0 (from pandas)
    Using cached https://files.pythonhosted.org/packages/cf/f5/af2b09c957ace60dcfac112b669c45c8c97e32f94aa8b56da4c6d1682825/python_dateutil-2.7.3-py2.py3-none-any.whl
  Collecting pytz&gt;=2011k (from pandas)
    Using cached https://files.pythonhosted.org/packages/30/4e/27c34b62430286c6d59177a0842ed90dc789ce5d1ed740887653b898779a/pytz-2018.5-py2.py3-none-any.whl
  Collecting six&gt;=1.5 (from python-dateutil&gt;=2.5.0-&gt;pandas)
    Using cached https://files.pythonhosted.org/packages/67/4b/141a581104b1f6397bfa78ac9d43d8ad29a7ca43ea90a2d863fe3056e86a/six-1.11.0-py2.py3-none-any.whl
  Installing collected packages: numpy, six, python-dateutil, pytz, pandas
  Successfully installed numpy-1.15.0 pandas-0.23.3 python-dateutil-2.7.3 pytz-2018.5 six-1.11.0
  
  Adding pandas to Pipfile's [packages]...
  Pipfile.lock not found, creating...
  Locking [dev-packages] dependencies...
  Locking [packages] dependencies...
  243, in get_dependencies
      legacy_results = self.get_legacy_dependencies(ireq)
    File "/usr/local/Cellar/pipenv/2018.7.1/libexec/lib/python3.7/site-packages/pipenv/patched/piptools/repositories/pypi.py", line 335, in get_legacy_dependencies
      self.resolver.resolve(reqset)
    File "/usr/local/Cellar/pipenv/2018.7.1/libexec/lib/python3.7/site-packages/pipenv/patched/notpip/_internal/resolve.py", line 107, in resolve
      self._resolve_one(requirement_set, req)
    File "/usr/local/Cellar/pipenv/2018.7.1/libexec/lib/python3.7/site-packages/pipenv/patched/notpip/_internal/resolve.py", line 264, in _resolve_one
      abstract_dist = self._get_abstract_dist_for(req_to_install)
    File "/usr/local/Cellar/pipenv/2018.7.1/libexec/lib/python3.7/site-packages/pipenv/patched/notpip/_internal/resolve.py", line 214, in _get_abstract_dist_for
      self.require_hashes
    File "/usr/local/Cellar/pipenv/2018.7.1/libexec/lib/python3.7/site-packages/pipenv/patched/notpip/_internal/operations/prepare.py", line 328, in prepare_linked_requirement
      abstract_dist.prep_for_dist(finder, self.build_isolation)
    File "/usr/local/Cellar/pipenv/2018.7.1/libexec/lib/python3.7/site-packages/pipenv/patched/notpip/_internal/operations/prepare.py", line 155, in prep_for_dist
      self.req.run_egg_info()
    File "/usr/local/Cellar/pipenv/2018.7.1/libexec/lib/python3.7/site-packages/pipenv/patched/notpip/_internal/req/req_install.py", line 486, in run_egg_info
      command_desc='python setup.py egg_info')
    File "/usr/local/Cellar/pipenv/2018.7.1/libexec/lib/python3.7/site-packages/pipenv/patched/notpip/_internal/utils/misc.py", line 698, in call_subprocess
      % (command_desc, proc.returncode, cwd))
  pipenv.patched.notpip._internal.exceptions.InstallationError: Command "python setup.py egg_info" failed with error code 1 in /var/folders/y1/7zsj8_x973n4xjwg5gg6s53jr4zz65/T/tmp6ghbw5_fbuild/email/
  </code></pre>
  
  <p>No idea what's going on to cause this. Any thoughts?</p>