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 fixed this by setting a done-time for each of them using this script:
```
#!/bin/bash
set -e

for ISSUE_ID in $(ent list state=done done-time=9999-01-01T00:00:00-06:00.. | grep '  ' | cut -f 1 -d ' '); do
    UTIME=$(PAGER='' git log -n1 --pretty=format:%at%n entomologist-data -- ${ISSUE_ID}/state)
    DATETIME=$(date --rfc-3339=seconds --date="@${UTIME}")
    ent done-time ${ISSUE_ID} "${DATETIME}"
done
```