Log Message:
py-notebook: updated to 6.4.11

6.4.11

Bugs fixed

- Update further to ipykernel comm refactoring

Maintenance and upkeep improvements

- Add testpath to the test dependencies.
- Temporary workaround to fix js-tests related to sanitizer js loading by phantomjs
- Use place-hold.it instead of plaecehold.it to create image placeholders
- Migrate to python 3.7+