Inherit decorator from superclass.

If the class itself does not have a decorator, try the superclass.
Merge remote-tracking branch 'upstream/master'
Fixed dummy mongoid config.
Bump minitest-rails development dependency

Draper should depend on the released versions of minitest-rails.
Version ~> 1.0 for Rails 3.0-4.0, and ~> 2.0 for Rails 4.1+.
Remove minitest-rails require

The mintest/rails require should only be in the test helper.
This code is here to deal with very old versions of minitest-rails,
but Draper should rely on the 1.0+ released versions.
These checks are very outdated, and worse, can introduce other bugs.
Use load hook for minitest integration

Unlike RSpec, Minitest doesn't load the Spec DSL when loaded by Bundler,
so loading the integration in the Railtie can be problematic.
Switch to a load hook so that the integration can be loaded whenever
minitest-rails is loaded, which it may not be during Draper initialization.
Update .travis.yml

Travis has chanced some stuff, new Rubies have come out, etc.
Merge pull request #617 from iliabylich/master

Fix dummy mongoid config.
Merge pull request #622 from blowmage/minitest-rails-release

Update minitest-rails integration
Fix allow failures syntax

Whoops. I thought I had it right, but I didn't.
Merge branch 'master' of github.com:drapergem/draper
Merge pull request #584 from mschuerig/master

Inherit decorator from superclass.
Draper.undecorate safely undecorates any object

This allows you to pass any object to Draper.undecorate knowing you will get the original object back
even if the object passed in does is not already decorated.

Closes #600