message: Add "unanticipated" wording for regressions
diff: @@ -29,9 +29,9 @@ to approve the PR by issuing `@bors` commands like the ones above
  ## Reverts
  -If a merged PR is found to have caused a meaningful regression, the best policy
  -is to revert it quickly and re-land it later once a fix and regression test are
  -added.
  +If a merged PR is found to have caused a meaningful unanticipated regression,
  +the best policy is to revert it quickly and re-land it later once a fix and
  +regression test are added.
  A "meaningful regression" in this case is up to the judgment of the person
  approving the revert. As a rule of thumb, this would be a bug in a stable
  