:arrow_up: Bump nbconvert from 5.5.0 to 6.4.0
:arrow_up: Bump nbconvert from 5.5.0 to 6.4.0

Bumps [nbconvert](https://github.com/jupyter/nbconvert) from 5.5.0 to 6.4.0.
- [Release notes](https://github.com/jupyter/nbconvert/releases)
- [Commits](https://github.com/jupyter/nbconvert/compare/5.5...6.4.0)

---
updated-dependencies:
- dependency-name: nbconvert
  dependency-type: indirect
  update-type: version-update:semver-major
...

Signed-off-by: dependabot[bot] <5bdcd3c0d4d24ae3e71b3b452a024c6324c7e4bb@github.com>
natl/fractaldna