Changed array_walk to foreach (Zend\Stdlib\Hydrator\ArraySerializable)

The data array is manipulated while traversing it. This does not work
with array_walk.

See PHP documentation:
http://www.php.net/manual/en/function.array-walk.php
Resolves #4258
Merge pull request #4259 from tux-rampage/hotfix/4258

Hotfix: Changed array_walk to foreach in Zend\Stdlib\Hydrator\ArraySerializable
Merge branch 'hotfix/4259'

Close #4259
Fixes #4258