E3D Chinese extruder fan duct

Remix of a very nice fan shroud. This is made to fit an E3D clone v5/6 extruder. Made edits so that it doesn't fall off a Kossel because of the fast head acceleration. Added top tab so the shroud locks in between the top fins, made the opening for the heatsink tighter so that it holds on firmly, and reduced the screw holes so that M3 screws can directly be threaded for the 40mm fan.

Short version grips the heatsink even tighter, allows for a 40x40x20mm fan to fit under the carriage. Picture i