Immediately refresh viewer for live-updates

Our applyUpdates() puts/deletes annotations into the viewer.
But for the stream page, because there was no scope digest cycle
it seemed that the UI was reacting very slow to show the annotations.

This one-liner just creates a digest cycle in these scenarios.
The user experience is a magnitude better with this in the stream page

Fix #1455
Merge pull request #1461 from hypothesis/1455-refresh-viewer-immediately

Immediately refresh viewer for live-updates