postgresql: security bump to version 9.6.6

postgresql: security bump to version 9.6.6

Fixes the following security issues:

CVE-2017-12172: Start scripts permit database administrator to modify
root-owned files.

CVE-2017-15098: Memory disclosure in JSON functions.

CVE-2017-15099: INSERT ... ON CONFLICT DO UPDATE fails to enforce SELECT
privileges.

See the announcement for more details:
https://www.postgresql.org/about/news/1801/

While we're at it, also add a hash for the license file.

Signed-off-by: Peter Korsgaard <peter@korsgaard.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>