flake8
passed.
JSHint
passed.
Add a couple missing Markdown extensions for e-mail rendering.
Review Request #8992 — Created June 4, 2017 and submitted
The Markdown e-mail rendering code wasn't correctly rendering lists or strings with double-underscores separating words, due to missing a couple of extensions. This adds those missing extensions, bringing some consistency.
Tested the e-mail previews before and after this change. Saw that the
Markdown had rendered incorrectly before in these cases, but rendered
correctly after.
