Instant < Interval breaks transitivity

[frenchy64]

Related #69

This should be false.

(let [interval-1-2 (j/interval 1 2)
      interval-3-4 (j/interval 3 4)
      interval-1-3 (j/interval 1 3)
      instant-1 (j/instant 1)
      instant-2 (j/instant 2)
      instant-3 (j/instant 3)]
  (is (not (j/not-after? instant-1 interval-1-3 instant-2 interval-1-3 instant-1))))