Thread: pgsql: doc: mention pg_upgrade extension script

doc:  mention  pg_upgrade extension script

Since commit e462856a7a, pg_upgrade automatically creates a script to
update extensions, so mention that instead of ALTER EXTENSION.

Backpatch-through: 9.6

Branch
------
REL_14_STABLE

Details
-------
https://git.postgresql.org/pg/commitdiff/9268fc34526427a48bc27b5ac4727c7fb4cddf7a

Modified Files
--------------
doc/src/sgml/ref/pgupgrade.sgml | 5 +++--
1 file changed, 3 insertions(+), 2 deletions(-)