slate config: focus bindings match vim motions

the cmd+shift+[hjkl] bindings to switch window focus has j/k going in the other's direction.

in other words:
- j goes down in vim, it was set to switch focus up one window.
- k goes up in vim, it was set to switch focus down one window.
Merge pull request #1 from unixsuperhero/patch-1

slate config: focus bindings match vim motions