fixed: lineman grunt

the refactoring of lineman cli into a bunch of coffeescript files (e65f78619584fcbdc4945bec10e5dbf2d64f0f2e) broke a bunch of stuff related to running grunt directly from the lineman cli. fix these problems:

1. typo in the command (`arguments_` rather than `arguments`)
2. make the path the gruntfile correct again (no longer at the root)