added two case 
added two case 

sync up with
https://github.com/exercism/xruby/blob/master/exercises/gigasecond/gigasecond_test.rb
exercism/xswift,masters3d/xswift,robtimp/xswift,masters3d/xswift,robtimp/xswift,exercism/xswift,exercism/xswift,robtimp/xswift,masters3d/xswift