IPython notebooks in old format (v3)

[tiangolo]

When I open the example notebooks I get a notification saying that they are in an older format (v3) and that they could be updated to (v4):

This notebook has been converted from an older notebook format (v3) to the current notebook format (v4). The next time you save this notebook, the current notebook format will be used. Older versions of IPython may not be able to read the new format. To preserve the original version, close the notebook without saving it.