Bump nbsphinx from 0.5.1 to 0.6.0

Bumps [nbsphinx](https://github.com/spatialaudio/nbsphinx) from 0.5.1 to 0.6.0.
- [Release notes](https://github.com/spatialaudio/nbsphinx/releases)
- [Changelog](https://github.com/spatialaudio/nbsphinx/blob/master/NEWS.rst)
- [Commits](spatialaudio/nbsphinx@0.5.1...0.6.0)

Signed-off-by: dependabot-preview[bot] <[email protected]>

Author: dependabot-preview[bot]

poetry.lock

@@ -132,7 +132,7 @@ pytest-xdist = "^1.31.0"
 pytest = "^5.3.4"
 freezegun = "^0.3.14"
 responses = "^0.10.9"
-nbsphinx = "~0.5"
+nbsphinx = "~0.6"
 aioresponses = "^0.6.2"
 moto = "==1.3.14"
 fakeredis = "^1.4.0"