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The example used in the documentation is outdated as well.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
------
REL_10_STABLE

Details
-------
https://git.postgresql.org/pg/commitdiff/5dd7f5cecf2c9f4f90d5031671acf31e4292a271

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