Fix config files in ancestor dirs are ignored if another exists in home

This fixes a bug below:

* You have `~/.rubocop.yml` in your home directory
* There is `project/.rubocop.yml`
* There is `project/example.rb`
* Execute `rubocop` in `project` directory

In this situation, `~/.rubocop.yml` is always used and `project/.rubocop.yml` is never used.