Cannot navigate between sections using up/down arrow keys in Edge

[jasonbekolay]

This can be reproduced on the mobiledoc-kit demo using Edge 17 on Windows. The steps are:

1. Create a document with at least 2 sections
2. With the cursor in the first section, attempt to navigate to second section by pressing ⬇️- the cursor will not move to the next section
3. With the cursor in the second section, attempt to navigate to the first section by press ⬆️- the cursor will not move to the first section

However, navigating between sections with the left and right arrow keys works fine. If you are at the end of the first second and press ➡️, the cursor will move to the second section and vice versa.

[mixonic]

@jasonbekolay thanks for this report.