pgsql: doc: adjust libpq wording to be neither/nor

doc: adjust libpq wording to be neither/nor

Reported-by: postgresql@cohi.at

Discussion: /messages/by-id/155419437926.737.10876947446993402227@wrigleys.postgresql.org

Backpatch-through: 9.4

Branch
------
REL9_4_STABLE

Details
-------
https://git.postgresql.org/pg/commitdiff/f4daf89582196596b947b9be96394a1f63a986dc

Modified Files
--------------
doc/src/sgml/libpq.sgml | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)