pgsql: doc: Add PERIOD to ALTER TABLE reference docs

doc: Add PERIOD to ALTER TABLE reference docs

Commit 89f908a6d0a documented foreign keys with PERIOD in the CREATE
TABLE docs, but not in ALTER TABLE.  This commit adds the new syntax
to the ALTER TABLE docs.

Author: Paul A. Jungwirth <pj@illuminatedcomputing.com>
Discussion: https://www.postgresql.org/message-id/57ea0668-5205-426e-b934-efc89f2186c2@illuminatedcomputing.com

Branch
------
master

Details
-------
https://git.postgresql.org/pg/commitdiff/d56af4c882e28a4dd91f96b66db6e5861b7b3f86

Modified Files
--------------
doc/src/sgml/ref/alter_table.sgml | 2 +-
1 file changed, 1 insertion(+), 1 deletion(-)