The done-time thing is implemented and merged, but many issues in our
database were marked Done before this change, so they have no `done_time`.

I think i want to fix this by setting a done-time for each of them using
something like:
```
for ISSUE_ID in $(ent list state=done done-time=9999-01-01T00:00:00-06:00.. | grep '  ' | cut -f 1 -d ' '); do
    # use `git log` on the issue's state file to find when it got marked Done
    ent done-time ${ISSUE_ID} ${TIME}
done
```