php: upgrade to 5.5.20

Among many fixes since 5.5.15, the following security issues were fixed:

CVE-2014-8142
CVE-2014-3710
CVE-2014-3669
CVE-2014-3670
CVE-2014-3668
CVE-2014-3538
CVE-2014-3587
CVE-2014-2497
CVE-2014-5120
CVE-2014-3597

For more details please see the upstream changelog:

  http://php.net/ChangeLog-5.php



Signed-off-by: Paul Eggleton <paul.eggleton@linux.intel.com>