pgsql: Fix typo in sslmode documentation

Fix typo in sslmode documentation

Per bug #6089, noted by Sidney Cadot

Branch
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REL9_0_STABLE

Details
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http://git.postgresql.org/pg/commitdiff/1e7b52d753f84ed46095a68f23e992a95e41f13f

Modified Files
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doc/src/sgml/libpq.sgml | 2 +-
1 files changed, 1 insertions(+), 1 deletions(-)