package/postgresql: bump to version 11.2

Fixes a long standing fsync issue and a number of other bugs:
https://www.postgresql.org/docs/11/release-11-2.html

https://wiki.postgresql.org/wiki/Fsync_Errors



The hash of the license file is only changed due to a year update:

-Portions Copyright (c) 1996-2018, PostgreSQL Global Development Group
+Portions Copyright (c) 1996-2019, PostgreSQL Global Development Group

Signed-off-by: Peter Korsgaard <peter@korsgaard.com>
Reviewed-by: Peter Seiderer <ps.report@gmx.net>
[Thomas: update commit log to explain why the license file hash has
changed, as repoted by Peter Seiderer]
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>