Source text in cell should include citation.

[dmyersturnbull]

When I insert a citation into a Markdown cell, I get the raw text <cite data-cite="undefined"></cite> (which is then rendered as the author's name and year). This is how it's stored in the .ipynb file:

   "source": [
    "<cite data-cite=\"undefined\"></cite>"
   ]

The raw text should include the author and year of the paper, a DOI, or something else.