zf-content-negotiation config key updates

Ran into an issue of `zf-content-negotiation` config not being read and noticed the keys had changed... found these unchanged references!

Referenced Change(s):
https://github.com/zfcampus/zf-content-negotiation/blob/master/src/ZF/ContentNegotiation/Factory/AcceptFilterListenerFactory.php

https://github.com/zfcampus/zf-content-negotiation/blob/master/src/ZF/ContentNegotiation/Factory/ContentTypeFilterListenerFactory.php#L33