Infos: Works with Python 3.6 too.

Hi,

Lovely idea!
Just FYI, it's also working with Python 3.6
Now that pip installs PyQt5, I just had to remove PySide (which is not 3.6 compliant) from the requirements.

```bash
# inside an env
git clone https://github.com/EricTRocks/pyflowgraph.git
cd pyflowgraph
vim setup.py # remove the PySide dep.
pip install --editable .
python tests/twoNodes.py
```

Thanks a lot


 