Some Windows users are used to launch files without specifying a command,
e.g.::

    > my-script.py

This works in the shell because Windows will automatically choose an
command based on file association, and with newer Python versions, the Py
Launcher (py.exe) automatically chooses the correct Python based on
shebang-parsing.

A similar syntax, unfortunately, does not currently work in Pipenv::

    > pipenv run my-script.py

Since my-script.py will be treated as a real application by the subprocess
module.

This patch catch Windows error 193 during subprocess initialization, and
fall back to use COMSPEC (shell=True) when it happens, to provide better
support for this use case.