php5 - security update

Several vulnerabilities were found in PHP, a general-purpose scripting
language commonly used for web application development.

The vulnerabilities are addressed by upgrading PHP to the new upstream
version 5.6.20, which includes additional bug fixes. Please refer to the
upstream changelog for more information:

• 
  https://php.net/ChangeLog-5.php#5.6.20

For the stable distribution (jessie), these problems have been fixed in
version 5.6.20+dfsg-0+deb8u1.

We recommend that you upgrade your php5 packages.