review-trigger asks for too many reviewers

[mutantcornholio]

Introduced in #60, there's the logic that upon any change re-requests reviews from everyone who has previously approved the PR.

The logic is written separately from review-bot (which IMO shouldn't be the case), and might require a too many reviewers, like in this case: #549 (comment).

While limiting amount of requested reviewers might seem like a good option, there's a possibility that a bunch of people with read permissions will approve the review first, then after pushing some changes, only their reviews will be re-requested.

This should be a functionality of review-bot itself, instead of being a part of review-trigger