more durable quick change tool holder

I made it thicker so it is less easy to break. Also I added a modifier mesh to make that area have more perimeters to be more durable.
Step file included.

[OnShape link](https://cad.onshape.com/documents/7d7d2d697c9197954b2beea0/w/2de4d757528f75c334302766/e/e827e88fb1974beaaf20080d)