Shown Example Is Not Appropriate for arrays--callback-return

[4.6 in Readme](https://github.com/airbnb/javascript#arrays--callback-return)
last example is shown as
```
inbox.filter((msg) => {
const { subject, author } = msg;
if (subject === 'Mockingbird') {
return author === 'Harper Lee';
}
return false;
});
```

but its not a example of `arrays--callback-return`, its illustrate `avoid of else`, when using return statement.

Start in the README's arrays--callback-return section, linked in the issue, and review the final example against that section's stated purpose. Update the example so it demonstrates the intended rule, then check the rendered README to confirm the example is appropriate and the surrounding guidance remains consistent.

Written by the indexing model from the issue text.