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The example used in the documentation is outdated as well.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_3_STABLE

Details
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https://git.postgresql.org/pg/commitdiff/4b2fb124d1d998b159a2f891c15fe12f6372e5ed

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