[Cache] Superfluous import of PhpFilesAdapter in Php Array Cache Adapter Documentation

[stollr]

In the first code example in the Php Array Cache Adapter documentation there is this line:

use Symfony\Component\Cache\Adapter\PhpFilesAdapter;

But this class is never used. Instead an object of class FilesystemAdapter (which is not imported) is instantiated

// a backup adapter, if you set values after warmup
new FilesystemAdapter()

I guess that something is mixed up there. Can somebody look into it?