Fix a build error

This commit fixes the following build error.

```console
% bundle exec rspec spec/project_spec.rb
(snip)

Failures:

  1) RuboCop Project Changelog entry contributor name has a unique contributor name
     Failure/Error: expect(contributor_names.uniq.size).to eq contributor_names.size

       expected: 576
            got: 572

       (compared using ==)

     Shared Example Group: "has Changelog format" called from
     ./spec/project_spec.rb:227
     # ./spec/project_spec.rb:195:in `block (5 levels) in <top (required)>'

Finished in 2.61 seconds (files took 1.55 seconds to load)
25 examples, 1 failure

Failed examples:

rspec ./spec/project_spec.rb:194 # RuboCop Project Changelog entry
contributor name has a unique contributor name
```

CHANGELOG.md

@@ -6167,8 +6167,4 @@
 [@ydah]: https://github.com/ydah
 [@chrisseaton]: https://github.com/chrisseaton
 [@nobuyo]: https://github.com/nobuyo
-[@nobuyo]: https://github.com/nobuyo
-[@nobuyo]: https://github.com/nobuyo
 [@johnny-miyake]: https://github.com/johnny-miyake
-[@nobuyo]: https://github.com/nobuyo
-[@nobuyo]: https://github.com/nobuyo