a matplotlib sphinx extension has moved into ipython

This causes a warning when I build sampledoc.

```
 MatplotlibDeprecationWarning: 
The Sphinx extension ipython_console_highlighting has moved from
matplotlib to IPython, and its use in matplotlib is deprecated.
Change your import from 'matplotlib.sphinxext.ipython_directive' to
'IPython.sphinxext.ipython_directive.
```

The change should be made in `conf.py` in sampledoc.
