Navigation breaks if iframe is the last line of a md file

[MaxGhenis]

Describe the bug
When an iframe is the last line of a md file, without a trailing new line, some page navigation breaks.

To Reproduce
Steps to reproduce the behavior:

1. jb create jb; cd jb
2. Add an iframe to the last line of intro.md, e.g.:

<iframe src="https://docs.google.com/spreadsheets/d/e/2PACX-1vQQoN_MKQqvDnUQjQHdCEISGkHYGgsSZVvHOWcv6qia260XbftP3aRh8FsPTXO-mJ8NioM7iSbNouTo/pubhtml?widget=true&amp;headers=false"></iframe>

3. jb build .
4. Open _build/html/intro.html, which looks like this:

Expected behavior
This, which is produced when I add a new line to the end of the file.

Environment (please complete the following information):

• Python 3.7.7
• Output of jupyter-book --version:

Jupyter Book: 0.7.1
MyST-NB: 0.8.3
Sphinx Book Theme: 0.0.31
MyST-Parser: 0.8.2
Jupyter-Cache: 0.2.2

[choldgraf]

I think I just fixed this in #817 - wanna try this again on master and see if it fixes your problem?

[MaxGhenis]

I'm getting the same result after running pip install git+https://github.com/executablebooks/jupyter-book.git and then jb clean . and jb build ..

[choldgraf]

hmmm I just tried this on the master branch of jupyter book and it looked fine to me. This is what my intro.md looked like:

Welcome to your Jupyter Book
============================

This is a small sample book to give you a feel for how book content is
structured.

Check out the content pages bundled with this sample book to get started.

<iframe src="https://docs.google.com/spreadsheets/d/e/2PACX-1vQQoN_MKQqvDnUQjQHdCEISGkHYGgsSZVvHOWcv6qia260XbftP3aRh8FsPTXO-mJ8NioM7iSbNouTo/pubhtml?widget=true&amp;headers=false"></iframe>

is that how yours looked?

[choldgraf]

ahhh nevermind, I just saw your point about "newline". OK I can replicate this if there is no blank line on the page

[choldgraf]

ok I think that #836 fixes this, wanna upgrade on master and try again?

[MaxGhenis]

That did it, thanks!

[choldgraf]

yahoo!