Upgrade sphinx and nbsphinx

[rsokl]

Partially addresses #140 but adding the copy button is blocked by: https://github.com/choldgraf/sphinx-copybutton/issues/71

[mgeier]

You don't seem to actually upgrade nbsphinx though, right?

If you do upgrade to nbsphinx release 0.6.0, you should consider updating your usage of nbsphinx_custom_formats, see https://nbsphinx.readthedocs.io/en/0.6.0/custom-formats.html and spatialaudio/nbsphinx#408.

[rsokl]

Ah! Good catch. I had temporarily rolled back the upgrade and exported my environment at the wrong time.

I'll be sure to fix that and to adjust my usage of nbsphinx_custom_formats

[rsokl]

@alexding123 heads-up