Collection shouldn't have to need a serializer in case of Resource collection

[rgazelot]

The Collection::__construct() need a SerializerInterface as second argument, but if the $data argument is an array of Resource object, this interface is never used. It should be nullable in order to fill the Collection with an array of Resource objects.

[tobyzerner]

This is fixed in #119

[rgazelot]

@tobscure Great! I would have to have a better reading about the PRs.