Fix wording in attributes_for deprecation warning

[fixes #181]
Version 2.9.1
Add ruby version requirement to gemspec
Merge pull request #184 from rwz/patch-1

Add ruby version requirement to gemspec
Remove attributes_for deprecation warning

[fixes #182]
Fix issue reference number in changelog
Version 2.9.2
Specify a ruby version compatible with rbenv
Load schematics through Fabricator.schematic in StepFabricator

[fixes #185]
Version 2.9.3
Convert Manager to singleton
Delegate clear and empty? to schematics
Raise UnfabricatableError when resolving classes
Create standard exception string in DuplicateFabricatorError
Move Fabricate class to separate file
Merge Fabrication::Fabricator with Fabricate class
Remove patch-level specification in .ruby-version
Bundle update
Update rbx version in travis.yml
Add rake task to list registered fabricators

[closes #187]

Thanks to Skye Shaw (https://github.com/sshaw) for the contribution!