Usage of mixed spelling of configuration keys make them overwrite each other

[func0der]

The mixed usage of 'accept-whitelist' and 'accept_whitelist' makes them overwrite each other.
Same goes for 'content-type-whitelist' and 'content_type_whitelist'.

The same goes probably for all options defined here:

zf-content-negotiation/test/ContentNegotiationOptionsTest.php

Lines 17 to 20 in 1875fe3

	'accept-whitelist' => ['accept-whitelist', 'accept_whitelist'],
	'content-type-whitelist' => ['content-type-whitelist', 'content_type_whitelist'],
	'x-http-method-override-enabled' => ['x-http-method-override-enabled', 'x_http_method_override_enabled'],
	'http-override-methods' => ['http-override-methods', 'http_override_methods'],

mixed usage should be deprecated in next major, but a fix is needed now.