Explicitly cast sudoers content to Array

Explicitly casting to an array in the template allows omitting the
array in the declaration if only one element is present. This is the
usual behavior for attributes accepting arrays.
Merge pull request #4 from bkkrw/master

Explicitly cast sudoers content to Array
Merge pull request #5 from dieterdemeyer/master

Redesign of sudo configuration
Better spec helper
Fix rspec deprecations