It's mild nutrient burn. You've got your plants pushed pretty hard with nutrients. It's ok if it stays like that but if it progresses down the leaf tip and curls upward that's more substantial nutrient burn.
probably a slight imbalance in either your feed or your ph :) I would double check everything and keep eye on her she might need but more feed or bit less if your following a feed table this should not really happen ? are you using anything new or ? nice looking bud though:) congrats