Fix ping stale reviewers on subsequent reviews

[jablko]

#79 put mostRecentReview.reviewedAbbrOid in the ping stale reviewers comment tag however .sort((l, r) => l.date.localeCompare(r.date))[0] in fact returns the least-recent review https://github.com/DefinitelyTyped/dt-mergebot/pull/79/files#diff-0dfef229af227cfaffa9c063923ac5b13c53e14422a6147d11bb95c28d98f37eR204

Since there are never any new least-recent reviews this makes that part of the tag impotent: subsequent reviews get the same tag.

This PR replaces min() with max() to get the behavior that presumably was intended.

[elibarzilay]

I'm confused here. The current code in pr-info chooses the most recent review for each reviewer, and then the code that your changing here takes the earliest of these which I think makes sense (but not sure). With this change, it would potentially make more nagging notifications when there are new reviews that become stale--??

One thing that is definitely missing (and would help clarify the above) is if you have a specific PR in mind where this change can be demonstrated (and used as a new test).

[elibarzilay]

Why are you dropping the reviewers' hash too?

[jablko]

A change in reviewers implies a change in reviewedAbbrOid, which the tag already contains, because the only way to change the stale reviewers is for a new review to become stale.

[jablko]

I added 49699 as a test (I had to edit it slightly because the CI isn't passing today).

I ran create-fixture 49699, then changed the checkSuite.conclusion from "FAILURE" to "SUCCESS".

1. ExE-Boss and rbuckton both reviewed 54b22fd
2. The author pushed new commits on Jan 1
3. The bot pinged ExE-Boss and rbuckton (stale-ping-54b22fd)
4. ExE-Boss reviewed 9ba9fd on Jan 15
5. The author pushed new commits
6. If the tests pass, the bot re-pings ExE-Boss and rbuckton (stale-ping-9ba9fdd)

The most recent reviews are

dt-mergebot/src/_tests/fixtures/49699/derived.json

Lines 126 to 137 in b8021e7

	{
	"type": "stale",
	"reviewer": "ExE-Boss",
	"date": "2021-01-15T07:34:48.000Z",
	"abbrOid": "9ba9fdd"
	},
	{
	"type": "stale",
	"reviewer": "rbuckton",
	"date": "2020-12-08T01:35:34.000Z",
	"abbrOid": "54b22fd"
	}

If we use the min() of these (current behavior) then the bot won't re-ping stale reviewers because all pings get the same tag, stale-ping-54b22fd from the min() review.

I confirmed that switching from max() back to min() does cause the test fail, because the bot doesn't re-ping after the latest commits.