Add bool to btree_gist documentation
Commit
57e3c516 added bool opclass to btree_gist, but update the list of
data types in docs to reflect this change.
Reported-by: Pavel Luzanov
Discussion: https://postgr.es/m/CAE2gYzyDKJBZngssR84VGZEN=Ux=V9FV23QfPgo+7-yYnKKg4g@mail.gmail.com