Flush figures with new backend name

[shaperilio]

Earlier this year, the name of the backend used by matplotlib changed. See the change at ipykernel and ipython. This effectively makes ipywidgets not call flush_figures anymore and so interactives with plots stopped working (see this old issue).

This change fixes that so flush_figures is called again.

[github-actions]

👈 Launch a binder notebook on branch shaperilio/ipywidgets/master

[jasongrout]

Thanks!

Confirmed the problem and that this solution works with currently released set of packages.

[jasongrout]

@meeseeksdev please backport to 7.x

[jasongrout]

The backport of this PR, #3278, was just released in ipywidgets 7.6.5. Thanks again for reporting and fixing this!

[ianhi]

@shaperilio thanks for the fix! - but I also want to make sure that you're aware of the ipywidget based backend for matplotlib: ipympl. It should have even better performance as well as allow mouse interactions such as zoom and pan. You can try out on binder here https://mybinder.org/v2/gh/matplotlib/ipympl/stable?urlpath=%2Flab%2Ftree%2Fexamples%2Fipympl.ipynb which should have some example of it working with ipywidges

[shaperilio]

Thanks @ianhi; I'll take a look!