Markdown Heading in Jupyter Notebook can break offline mode

[maegul]

In the Jupyter notebook, having a markdown heading # Plotly creates an HTML element with id=Plotly which then prevents the insertion of plotly.js using init_notebook_mode()

Unlikely error, but it can and does happen.

Is it possible to have this error not pass silently?

[jonmmease]

Good observation! I think we can just use something less common for our window.Plotly variable in init_notebook_mode().

[jonmmease]

worked around in #1250 which will be released in version 3.4.0