Insert a newline at EOF of CHANGELOG.md

This commit fixes the folowing CI failure.

```console
% bundle exec rake

(snip)

  1) RuboCop Project changelog has newline at end of file
     Failure/Error: expect(changelog.end_with?("\n")).to be true

       expected true
            got false
     # ./spec/project_spec.rb:91:in `block (3 levels) in <top (required)>'
```

https://circleci.com/gh/rubocop-hq/rubocop/42229

CHANGELOG.md

@@ -3874,4 +3874,4 @@
 [@unasuke]: https://github.com/unasuke
 [@elmasantos]: https://github.com/elmasantos
 [@luciamo]: https://github.com/luciamo
-[@dirtyharrycallahan]: https://github.com/dirtyharrycallahan
+[@dirtyharrycallahan]: https://github.com/dirtyharrycallahan