doc: Update pg_constraint.conexclop docs for WITHOUT OVERLAPS
Fixup for commit
fc0438b4e80.
Author: Paul A. Jungwirth <pj@illuminatedcomputing.com>
Discussion: https://www.postgresql.org/message-id/
57ea0668-5205-426e-b934-
efc89f2186c2@illuminatedcomputing.com