fix missing psutil dependency

[ont]

I have an error after installing zencad through pipx:

> pipx install --include-deps zencad
> zencad
Traceback (most recent call last):
  File "/home/ont/.local/bin/zencad", line 4, in <module>
    import zencad
  File "/home/ont/.local/pipx/venvs/zencad/lib/python3.7/site-packages/zencad/__init__.py", line 12, in <module>
    from zencad.visual import screen
  File "/home/ont/.local/pipx/venvs/zencad/lib/python3.7/site-packages/zencad/visual.py", line 2, in <module>
    import zencad.shower
  File "/home/ont/.local/pipx/venvs/zencad/lib/python3.7/site-packages/zencad/shower.py", line 14, in <module>
    import psutil
ModuleNotFoundError: No module named 'psutil'

Probably this patch will fix this error.

[mirmik]

Thank you!

[mirmik]

Hmm ... :)

But in reality, this dependence is not used and remained from the experiments. I will remove it in the next version.