Currently, the pytest tests fail, due to Network.show being called on Network instances that were initialised with notebook=False, meaning that Network.prep_notebook wasn't called and self.template remains as None. As Network.show's notebook argument defaults to True, it by default attempts to call self.template.render' and errors because None` doesn't have this method.

This PR changes show to default to notebook=False, which follows the pattern used in other methods. The pytest tests now pass.

If notebook=True really is the desired default for show, an alternative is to explicitly set notebook=False in the tests.