package/php: security bump to version 7.2.9

Version 7.2.8 fixed CVE-2018-12882, CVE-2018-14883 & CVE-2018-14851:
http://www.php.net/ChangeLog-7.php#7.2.8



Signed-off-by: Bernd Kuhls <bernd.kuhls@t-online.de>
Signed-off-by: Thomas Petazzoni <thomas.petazzoni@bootlin.com>