switch Node.traverse() to findall() to avoid deprecation warnings

[wpbonelli]

This should be OK to switch straight to .findall() with no need to try/except and fall back to .traverse() since sphinx requires docutils >= 0.18.1

[mgeier]

Thanks for this PR, and sorry for my very late response!

Before merging this, I would like to check which versions I want to support and re-activate the tests, see #495.

For now, I have silenced the warning (a1a56f5), which can be reverted once this is merged.

[mgeier]

I have finally checked which versions I want to support and I have re-activated the tests in #792.

Can you please re-base your PR and add a lower bound to our docutils dependency?

nbsphinx/setup.py

Line 27 in c5fbe13

'docutils',

[wpbonelli]

@mgeier sure! done.

[mgeier]

Thanks a lot!