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The example used in the documentation is outdated as well.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: /messages/by-id/153838692816.2950.12001142346234155699@wrigleys.postgresql.org
Backpatch-through: 9.3

Branch
------
REL9_6_STABLE

Details
-------
https://git.postgresql.org/pg/commitdiff/0353f48f0e7c85bc1a053710ed42ab23123b0b7c

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