Make --show-cops option aware of --force-default-config

[pocke]

Problem

Currently, --show-cops option is not aware of --force-default-config option. It always print a configuration for current directory.
So we need chdir to get a default configuration with --show-cops.

For example

$ cat .rubocop.yml
Layout/Tab:
  Enabled: false

$ rubocop --show-cops Layout/Tab --force-default-config
Layout/Tab:
  Description: No hard tabs.
  StyleGuide: "#spaces-indentation"
  Enabled: false
  IndentationWidth:

Solution

This change will make --show-cops option aware of --force-default-config.

---

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).
• Used the same coding conventions as the rest of the project.
• 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.
• All tests(rake spec) are passing.
• The new code doesn't generate RuboCop offenses that are checked by rake internal_investigation.
• The PR relates to only one subject with a clear title
  and description in grammatically correct, complete sentences.
• Updated cop documentation with rake generate_cops_documentation (required only when you've added a new cop or changed the configuration/documentation of an existing cop).

[bbatsov]

👍