pgsql: docs: use consistent markup for PostgreSQL

docs: use consistent markup for PostgreSQL

"PostgreSQL" should use <productname> markup consistenktly, so that
if we do apply styling on it it will be consistently applied. Fix
by renaming the one exception to the rule.

Discussion: /messages/by-id/F2EF5217-27A3-4962-9AE5-2E6C2CB3D0FF@yesql.se

Branch
------
master

Details
-------
https://git.postgresql.org/pg/commitdiff/0f85db92b9ea167d3b9e90f3fb5fb3b9a93babc2

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