Nocturne needs more than just a buff to his ultimate's cooldown. Buff Umbra Blades a little bit.
Whenever you jungle as Nocturne, one thing is certain: Umbra Blades isn't going to keep you sustained. Until you have a Vampiric Scepter, you are going to be recalling a lot and getting smacked up by jungle camps pretty hard in the meantime.
Add onto that that the tooltip for Umbra Blades doesn't even tell you how much you heal for each enemy hit, and you are left with a severe inconvenience when you can't calculate if you can survive a camp or not. Really annoying.
Can you make Nocturne's passive a tad more effective? It shouldn't make his laning any better, because using it optimally will require pushing.