Saving Workflows Example currently not working

As mentioned in https://github.com/miykael/nipype_tutorial/pull/77#issuecomment-385529548, the current [Saving Workflows](http://nipype.readthedocs.io/en/latest/users/saving_workflows.html) user documentation is not working in the notebook.

The corresponding notebook is [wip_saving_workflows.ipynb](https://github.com/miykael/nipype_tutorial/blob/master/notebooks/wip_saving_workflows.ipynb).