pgsql: Fix documentation of pgrowlocks using "lock_type" instead of"mo

Fix documentation of pgrowlocks using "lock_type" instead of "modes"

The example used in the documentation is outdated as well.  This is an
oversight from 0ac5ad5, which bumped up pgrowlocks but forgot some bits
of the documentation.

Reported-by: Chris Wilson
Discussion: https://postgr.es/m/153838692816.2950.12001142346234155699@wrigleys.postgresql.org
Backpatch-through: 9.3

Branch
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REL9_4_STABLE

Details
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https://git.postgresql.org/pg/commitdiff/2bedb0ec7953737c361c7d50849f1177d55c1a42

Modified Files
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doc/src/sgml/pgrowlocks.sgml | 18 +++++++++---------
1 file changed, 9 insertions(+), 9 deletions(-)