Using distinct is much faster than pluck here.
We should still probably memcached this result though since it will hardly ever change.
See comments under https://github.com/biola/profile-publisher/commit/afa4a50550aecdd3760a34df5f8f073ea1287764
Merge pull request #92 from biola/fix_person_index_performace

Improving performance on person index page.