Dashboard overview doesn't update with new metrics

**Gorse version**
v0.4.14 (gorse-in-one, per dashboard master version)

**Describe the bug**
The web dashboard only shows accurate metrics on startup. I've had it running for hours a couple of times but nothing changes.

**To Reproduce**
Simply start Gorse and insert some items/positively marked feedback. The 5 metrics on the overview page do not change.

**Expected behavior**
I expect the dashboard to be relatively real-time. I'm not sure what the metrics refresh period is, but it seemed to be stale for well over an hour.

**Additional context**
Is this period a configuration option I should be changing somewhere?