ensure parents of globbed files are added to dependencies

This should fix #107.  The problem appears to be that the "parent directory" of the globbed file is not being added to the dependencies.

For example if I have the following:

```css
@import "*.scss";
```

Each of the files found by the glob was being added to the dependencies, but the `stylesheets` directory was not.

Perhaps my implementation of `globbed_file_parent` is overly naive.