php-apc is deprecated

[Kiina]

While investigating why my piwik installation is so slow I saw that the images uses APC https://github.com/MarvAmBass/docker-piwik/blob/master/Dockerfile#L14

But a quick run of php -v reveals that the container runs php 5.6

PHP 5.6.20-0+deb8u1 (cli) (built: Apr 27 2016 11:26:05) 
Copyright (c) 1997-2016 The PHP Group
Zend Engine v2.6.0, Copyright (c) 1998-2016 Zend Technologies
    with Zend OPcache v7.0.6-dev, Copyright (c) 1999-2016, by Zend Technologies

It seems like APC isn't supported since php 5.5 and got replaced by OPcache. Maybe APC should be removed and OPcache configured:

http://www.php.net/manual/en/opcache.configuration.php