D300VS+ Improved Fan Duct

I found the original fan duct to be brittle, and had several break at the hole near the joint because of the thin arm. This is the same model with a widened arm. It doesn't get in the way of the manual extruder dial.

The same as [d300p_aero_fan_duct.stl](https://github.com/UltiBots/D300VS-PLUS/blob/master/d300p_aero_fan_duct.stl) but with a wider neck.