When I have that problem, I cut a half-inch-by inch piece of old innertube and glue it on the inside of the tire over the cut. You need a rubber glue that will stay soft after drying. I use O'Neill's neoprene wetsuit repair glue. I just happened to have it for my own wetsuit repair, but there must be other glues like it out there. This kind of repair helps prevent potential destructive road debris from working its way into your tire and tube.

Rich