Update shlex to be compatible with changes from python 3.6: https://docs.python.org/3/library/shlex.html
Those changes should fix issues I've encountered:
```
main.py:10: error: No overload variant of "list" matches argument types [shlex.shlex]
main.py:10: error: Unexpected keyword argument "punctuation_chars" for "shlex"
/usr/local/lib/mypy/typeshed/stdlib/3/shlex.pyi:29: note: "shlex" defined here
```
caused by
```python
list(shlex(string, posix=True, punctuation_chars=True))
```
