[Examples] Scrollbar example raises RuntimeError on exit

Running the example creates an interactive plot and the `RuntimeError` is only generated when I close the plot. Python 3.6.0, OSX.

```
(empty_py3_env)examples (master)$ python demo/basic/scrollbar.py
/Users/rahulporuri/.edm/envs/empty_py3_env/lib/python3.6/site-packages/chaco/array_data_source.py:123: FutureWarning: comparison to `None` will result in an elementwise object comparison in the future.
self._data = newdata
scrollrange: (-2.0, 10.0, 12.0, 1)
/Users/rahulporuri/.edm/envs/empty_py3_env/lib/python3.6/site-packages/chaco/axis.py:498: FutureWarning: comparison to `None` will result in an elementwise object comparison in the future.
for tickpos in mapped_tick_positions]))
/Users/rahulporuri/.edm/envs/empty_py3_env/lib/python3.6/site-packages/chaco/axis.py:499: FutureWarning: comparison to `None` will result in an elementwise object comparison in the future.
self._tick_label_list = tick_list
/Users/rahulporuri/.edm/envs/empty_py3_env/lib/python3.6/site-packages/chaco/axis.py:500: FutureWarning: comparison to `None` will result in an elementwise object comparison in the future.
self._tick_label_positions = self._tick_positions
/Users/rahulporuri/.edm/envs/empty_py3_env/lib/python3.6/site-packages/kiva/fonttools/font_manager.py:1308: UserWarning: findfont: Font family ['sans-serif'] not found. Falling back to Bitstream Vera Sans
(prop.get_family(), self.defaultFamily[fontext]))
/Users/rahulporuri/.edm/envs/empty_py3_env/lib/python3.6/site-packages/kiva/fonttools/font_manager.py:1318: UserWarning: findfont: Could not match (['Bitstream Vera Sans'], 'normal', None, 'normal', 500, 10.0). Returning /Library/Fonts/Andale Mono.ttf
UserWarning)
Exception ignored in: >
Traceback (most recent call last):
File "/Users/rahulporuri/.edm/envs/empty_py3_env/lib/python3.6/site-packages/enable/qt4/scrollbar.py", line 122, in __del__
File "/Users/rahulporuri/.edm/envs/empty_py3_env/lib/python3.6/site-packages/enable/qt4/scrollbar.py", line 115, in destroy
RuntimeError: wrapped C/C++ object of type QResizableScrollBar has been deleted
```