postgresql: bump version to 9.6.3 (security)

postgresql: bump version to 9.6.3 (security)

Three security vulnerabilities have been closed by this release:

CVE-2017-7484: selectivity estimators bypass SELECT privilege checks
CVE-2017-7485: libpq ignores PGREQUIRESSL environment variable
CVE-2017-7486: pg_user_mappings view discloses foreign server passwords

More details: https://www.postgresql.org/about/news/1746/

Signed-off-by: Vicente Olivert Riera <Vincent.Riera@imgtec.com>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>