Fix rest function

[icyrockcom]

rest is failing because it tries to read the array, but the input is an object that has _ key for the remainder of the arguments:

> require('yargs')(['a', 'b', 'c']).argv
{ _: [ 'a', 'b', 'c' ], '$0': '' }

Also upgraded yargs dependency to the latest version.

[paf31]

Thanks!