pgsql: Update size references in installation instructions to be a bit

Log Message:
-----------
Update size references in installation instructions to be a bit
more up-to-date with current versions.

Tags:
----
REL8_4_STABLE

Modified Files:
--------------
pgsql/doc/src/sgml:
installation.sgml (r1.325.2.3 -> r1.325.2.4)
(http://anoncvs.postgresql.org/cvsweb.cgi/pgsql/doc/src/sgml/installation.sgml?r1=1.325.2.3&r2=1.325.2.4)