ModuleNotFoundError when running installed packages
I am seeing this issue with lots of packages that have a command-line entry point (at least `pytest` and `honcho`):

```
$ pipenv --version
pipenv, version 3.2.0

$ pipenv install honcho
Installing honcho...
Collecting honcho
  Using cached honcho-0.7.1-py2.py3-none-any.whl
Installing collected packages: honcho
Successfully installed honcho-0.7.1

Adding honcho to Pipfile's [packages]...

$ pipenv run honcho
Traceback (most recent call last):
  File "<root>/.venv/bin/honcho", line 7, in <module>
    from honcho.command import main
ModuleNotFoundError: No module named 'honcho'
```
diff --git a/pipenv/cli.py b/pipenv/cli.py
index 3bf3ac09..b6723a84 100644
--- a/pipenv/cli.py
+++ b/pipenv/cli.py
@@ -440,6 +440,8 @@ def do_init(dev=False, requirements=False, skip_virtualenv=False, allow_global=F
 
 
 def pip_install(package_name=None, r=None, allow_global=False):
+    # Prevent invalid shebangs with Homebrew-installed Python: https://bugs.python.org/issue22490
+    os.environ.pop('__PYVENV_LAUNCHER__', None)
     if r:
         c = delegator.run('{0} install -r {1} --require-hashes -i {2}'.format(which_pip(allow_global=allow_global), r, project.source['url']))
     else:
['pipenv/cli.py']