Add filter to treat an object the same as a single array containing that object

[kpaulisse]

Overview

This pull request adds a filter to treat an object the same as a single array containing that object. This difference can appear between some versions of Puppet but it really doesn't reflect an actual difference.

With filter off, this is a difference:

old: { notify: "Service[foo]" }
new: { notify: [ "Service[foo]" ] }

With the filter turned on, the above example is not a difference.

Fixes #166

Checklist

• Make sure that all of the tests pass, and fix any that don't. Just run rake in your checkout directory, or review the CI job triggered whenever you push to a pull request.
• Make sure that there is 100% test coverage by running rake coverage:spec or ignoring untestable sections of code with # :nocov comments. If you need help getting to 100% coverage please ask; however, don't just submit code with no tests.
• If you have added a new command line option, we would greatly appreciate a corresponding integration test that exercises it from start to finish. This is optional but recommended.