pgsql: Doc: fix minor bug in CREATE TABLE example.

Doc: fix minor bug in CREATE TABLE example.

One example in create_table.sgml claimed to be showing table constraint
syntax, but it was really column constraint syntax due to the omission
of a comma.  This is both wrong and confusing, so fix it in all
supported branches.

Per report from neil@postgrescompare.com.

Discussion: https://postgr.es/m/151871659877.1393.2431103178451978795@wrigleys.postgresql.org

Branch
------
REL9_6_STABLE

Details
-------
https://git.postgresql.org/pg/commitdiff/f68b52c9f9965aad1b0b9f9f8f6c5d08021ce810

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