Fix errors in setup.py

I was getting the following error trying to install for development:

```
$ python setup.py install
Traceback (most recent call last):
  File "setup.py", line 19, in <module>
    python-modargs],
NameError: name 'python' is not defined
```

Turns out that "python-modargs" wasn't quoted in setup.py. That's now fixed.