Added spec to show array serialization doesn't work in integration specs

I have yet to find a solution to this, but I wanted to bring it up. 

This is the error:

    ActionController::Serialization::ImplicitSerializerTest#test_render_array_using_implicit_serializer:
    NoMethodError: undefined method `attributes' for #<ActiveModel::Serializer::ArraySerializer:0x00000002968c58>
        active_model_serializers/lib/active_model/serializer/adapter/json.rb:6:in `serializable_hash'
        active_model_serializers/lib/active_model/serializer/adapter.rb:20:in `to_json'
        .rvm/gems/ruby-2.1.2/gems/actionpack-4.1.6/lib/action_controller/metal/renderers.rb:96:in `block in <module:Renderers>'
        active_model_serializers/lib/action_controller/serialization.rb:18:in `block (2 levels) in <module:Serialization>'

I'm still investigating. I'll post a solution as soon as I find one.