Bump atom req to one with a fixed keymap

This bumps vim-mode's atom requirement to one with a fixed keymap that seems to fix a ton of open issues.

cc @kevinsawicki do I need anything else on the vim-mode side?

@jacobgardner can you make sure this branch still works on linux with the latest atom release? Everything should be 100% now.

@mcnicholls tests should be passing on this branch in win32 and I would :heart: if you could check. I imagine your pull is ready to go without further changes after this lands.