Update CircleCI badge for new repo URL

[tnir]

Badge and link are now dead as the GitHub repo URL has been changed from rubocop-hq to rubocop. CircleCI does not look like supporting redirecting from the old one to the current one.

Signed-off-by: Takuya Noguchi takninnovationresearch@gmail.com

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Before submitting the PR make sure the following are checked:

• Feature branch is up-to-date with master (if not - rebase it).
• Squashed related commits together.
• [n/a] Added tests.
• Updated documentation.
• [n/a] Added an entry to the CHANGELOG.md if the new code introduces user-observable changes.
• The build (bundle exec rake) passes (be sure to run this locally, since it may produce updated documentation that you will need to commit).

If you have created a new cop:

• [n/a] Added the new cop to config/default.yml.
• [n/a] The cop is configured as Enabled: pending in config/default.yml.
• [n/a] The cop documents examples of good and bad code.
• [n/a] The tests assert both that bad code is reported and that good code is not reported.
• [n/a] Set VersionAdded in default/config.yml to the next minor version.

If you have modified an existing cop's configuration options:

• [n/a] Set VersionChanged in config/default.yml to the next major version.

[pirj]

Thank you!