Fix an error when using changed_parameters by external library

[koic]

This PR fixes the following error when using changed_parameters in obsoletion.yml by external library.

NoMethodError: undefined method `merge' for
[{"cops"=>["Layout/SpaceAroundOperators", "Style/SpaceAroundOperators"],
"parameters"=>"MultiSpaceAllowedForOperators", "reason"=>"If your
intention was to allow extra spaces for alignment, please use `AllowFoy

          first.merge(second)
               ^^^^^^
/Users/koic/src/github.com/rubocop/rubocop-rails/lib/rubocop/rails/inject.rb:11:in `new'
/Users/koic/src/github.com/rubocop/rubocop-rails/lib/rubocop/rails/inject.rb:11:in `defaults!'
/Users/koic/src/github.com/rubocop/rubocop-rails/lib/rubocop-rails.rb:13:in `<top (required)>'

---

Before submitting the PR make sure the following are checked:

• The PR relates to only one subject with a clear title and description in grammatically correct, complete sentences.
• Wrote good commit messages.
• Commit message starts with [Fix #issue-number] (if the related issue exists).
• Feature branch is up-to-date with master (if not - rebase it).
• Squashed related commits together.
• Added tests.
• Ran bundle exec rake default. It executes all tests and runs RuboCop on its own code.
• Added an entry (file) to the changelog folder named {change_type}_{change_description}.md if the new code introduces user-observable changes. See changelog entry format for details.