Fix a build error
Fix a build error

This commits fix the following build error:

```console
Offenses:

lib/rubocop/cop/gemspec/test_files_assignment.rb:6:9: C: [Correctable]
InternalAffairs/CopDescription: Description should be started with
Checks instead of This cop ....
      # This cop checks that the `test_files` attribute is not set in a
      gemspec file. ...
      ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^

1364 files inspected, 1 offense detected, 1 offense autocorrectable
RuboCop failed!

Exited with code exit status 1
```

https://app.circleci.com/pipelines/github/rubocop/rubocop/6304/workflows/14e72f13-0aba-407d-8eb3-72b37ac210d4/jobs/220728

rrosenblum/rubocop,rrosenblum/rubocop,tejasbubane/rubocop,tejasbubane/rubocop,rrosenblum/rubocop,tejasbubane/rubocop