Use correct syntax for owning all files in a folder (#3510)

From the GitHub docs:

> # The `docs/*` pattern will match files like
> # `docs/getting-started.md` but not further nested files like
> # `docs/build-app/troubleshooting.md`.
> docs/*  [email protected]
>
> # In this example, @octocat owns any file in an apps directory
> # anywhere in your repository.
> apps/ @octocat