[Fix] Matplotlib arrow rendering

Starting from matplotlib = 3.5, pystencils' definition for 3D arrows is deprecated. Therefore, 3D stencils cannot be rendered anymore.
The exact issue is stated, e.g., here : https://github.com/matplotlib/matplotlib/issues/21688

Fixes #67 (closed)

added Bug label

requested review from @schottenhamml

assigned to @holzer

merged

mentioned in commit 04232aaa