K40 Exhaust Duct for 4" Blower

A quick remix of [JimmyBDesign's K40 ducting design](http://www.thingiverse.com/thing:1874500). Expanded the outlet port to 4", since I had a 4" blower and hose already handy. Should still fit in the same standard slot on the back of the K40 as the original. Printed mine in two parts mostly to limit the supports required.