.gitconfig.local should be the last thing in .gitconfig

Per the git documentation:

> The included file is expanded immediately, as if its contents had been
> found at the location of the include directive.

Which is to say that any settings in `.gitconfig` that appear *after*
the `include.path` setting will override settings in the included file.
Since `.gitconfig.local` settings should always override the defaults in
`.gitconfig`, the `core.include` directive should come last.