tests are now failing on master

platform : Mac OS X, 10.14.3
Python version : 3.7.3
Pip version ( if relevant ) : 9.0.3

I was getting test failures on a branch and so checkout master as a baseline. Turns out that's failing for me as well.

```bash
git clone git@github.com:linkedin/shiv.git
cd shiv
python3 setup.py venv
source activate
python3 setup.py develop
```
then

```bash
pip install tox
tox -e py37
```

gives
```
# check that the command successfully completed
assert result.exit_code == 0

# ensure the created file actually exists
assert output_file.exists()

# now run the produced zipapp
proc = subprocess.run(
[str(output_file)],
input=b"import hello;print(hello)",
stdout=subprocess.PIPE,
stderr=subprocess.PIPE,
shell=True,
env=os.environ,
)

> assert proc.returncode == 0
E assert 2 == 0
E + where 2 = CompletedProcess(args=['/private/var/folders/x_/h517ndbj2qx9m6ydt_vtsrv00000gn/T/pytest-of-ianmaclean/pytest-27/test_n...x83\xa0\x88\x08\x08\xe8&\x85\x11!B\x13\xc4\x92\xaf\x9f\xe9\xa9\xb6\xba7\xd6[\xde\xba\xe7.\x9e$\r$ip&\xe5 K\x8a\x82'\n").returncode

test/test_cli.py:189: AssertionError
```
doing some more digging to see exactly whats failing. pyz's built from the built shiv package seem to work fine.

Reproduce the failure using the setup commands and `tox -e py37`, then inspect `test/test_cli.py:189` and the subprocess output and return code. Compare this with the reported working pyz-built package to narrow down the failure. Done means the test passes and the py37 tox run completes successfully on the affected environment.

Written by the indexing model from the issue text.