AttributeError: 'module' object has no attribute 'split'

```
% sudo pip3 install -U python-apt
Collecting python-apt
Downloading python-apt-0.7.8.tar.bz2 (49kB)
100% |████████████████████████████████| 53kB 1.2MB/s
Complete output from command python setup.py egg_info:
Traceback (most recent call last):
File "", line 20, in
File "/tmp/pip-build-3wzlbss1/python-apt/setup.py", line 11, in
string.split(parse_makefile("python/makefile")["APT_PKG_SRC"]))
AttributeError: 'module' object has no attribute 'split'
```

So, even though I'm using pip3, the deprecated `string.split` call is in the code.