Github gutter marks do not reliably clear when git status is updated.

[avanrossum]

When changes to files are committed, the gutters do not consistently clear. It can be forced to clear by changing the focused tab, or by making and saving another edit.

Steps to reproduce:

1. Make changes
2. Save
3. Commit via CLI or desktop app
4. Gutter marks (may) remain
5. Edit and save, or toggle tab focus, gutter marks clear.