add rakefile (lowercase) to default config

[jethrodaniel]

We should also support rakefile when looking for Ruby files to
process.

As of rake-13.0.1

# rake/lib/rake/application.rb
DEFAULT_RAKEFILES = [
  "rakefile",
  "Rakefile",
  "rakefile.rb",
  "Rakefile.rb"
].freeze

---

Before submitting the PR make sure the following are checked:

• 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.
• Added an entry to the Changelog if the new code introduces user-observable changes. See changelog entry format.
• The PR relates to only one subject with a clear title and description in grammatically correct, complete sentences.
• Run bundle exec rake default. It executes all tests and RuboCop for itself, and generates the documentation.

[koic]

Can you add a chengelog entry and update spec/rubocop/target_finder_spec.rb?
e.g. #7895

[jethrodaniel]

Had no idea about spec/rubocop/target_finder_spec.rb, thanks.

I just forgot the change-log.

[koic]

👍