pgsql: docs: fix wording of REFRESH CONCURRENTLY manual page

docs: fix wording of REFRESH CONCURRENTLY manual page

Reported-by: Asim / apraveen@pivotal.io

Discussion: /messages/by-id/157076828181.26165.15231292023740913543@wrigleys.postgresql.org

Backpatch-through: 9.4

Branch
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REL_12_STABLE

Details
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https://git.postgresql.org/pg/commitdiff/56a459be51931838675b59b6be42ba1f20a8dbf1

Modified Files
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doc/src/sgml/ref/refresh_materialized_view.sgml | 4 ++--
1 file changed, 2 insertions(+), 2 deletions(-)