Revert "First part of a fix for #208."

This reverts commit 145b6d499db8038de0ff2574802f2b399e661b47.

This fix introduced an incompatibility with Rails 3.0.

We'll have to fix it in a different way for older Rails.
Fix serializer.as_json(nil)

This is the form that ActiveSupport 3.1 Object#to_json invokes.
Merge pull request #477 from gtd/fix-as-json-with-nil

Allow serializer#as_json to be called with nil
Fix type in Readme

proof https://github.com/rails-api/active_model_serializers/blob/0-8-stable/test/serializer_support_test.rb
Merge pull request #536 from icem/patch-1

Fix type in Readme
Fix ArraySerializer's output when falling back on DefaultSerializer

Change ArraySerializer's initialization of DefaultSerializer to pass
:root => false in order to avoid adding root keys to each of the
items in the array. This ensures consistent results between serializing
arrays of objects with serializers and arrays of objects without
serializers. Fixes #495.
Merge pull request #538 from mayhewluke/fix-array-output

Fix ArraySerializer's output when falling back on DefaultSerializer
Fix rbx in .travis.yml
Remove coveralls.

It's fine, but it's causing issues.