Update later.js

[ghost]

was failing with test var newDate = new Date('2014-02-28'); later.schedule({schedules: [{D:[1], M:[2], Y:[2014]},{D_a:[27], D_b:[29], M:[2], Y:[2014]}], exceptions: []}).isValid(newDate);

return !b || a.getTime() > b.getTime(); <-- a is null and so a.getTime() is blowing up

Bills fix is working a treat so far

[ilanbiala]

@oziee can you make these changes?

[niftylettuce]

Per my work with Bree, I have an updated fork of this package called @breejs/later. See https://github.com/breejs/later if you would like to file this PR there.