Update .gitmodules to reflect new directory structure

[zo0o0ot]

The gitmodules file still refers to the old directory structure, and that should be updated.

[zo0o0ot]

I have a PR open at #56 but I'm not sure if it's completely updated.

I may need to check this out:
https://stackoverflow.com/questions/913701/how-to-change-the-remote-repository-for-a-git-submodule