Allow to fail on ruby-head
Update Rubinius Gemfiles, Travis

Simplify the Gemfile setup for Travis by requiring version 2.2.5.

This commit updates the Travis version of Rubinius to 2.2.5+, which
includes the ruby standard library. Thus platform-specific Gemfile
configuration is no longer needed for Rubinius.

Also, Rubinius 2.2.5 does not work with sqilte3 1.3.9, so require
sqlite3 version 1.3.8 until it does.

:computer: To run the tests locally, you will need to use Rubinius
2.2.5.
Merge pull request #522 from teeparham/rubinius_2

Update Rubinius Gemfiles, Travis
Adds an example for using ArraySerializer under Render independently.
only require coverage_setup on CI
Use RAILS_VERSION on Gemfile
Use new ENV on travis
Test against ruby 2.1.1
test on rails 4.1
HasOne nil object should return [] under embedded key.

Ensure that @wrap_in_array is always respected when set to true even
when associated object is nil.
Use minitest 4.7.x on rails 3.2
Merge pull request #528 from arthurnn/travis_one_file

Few Travis configs
Merge pull request #524 from depy/master

Adds an example for using ArraySerializer under Render independently.
Add :only/:except options
Allow to define custom serializer for given class

.. by defining #active_model_serializer method on serialized object. Resolves #515.