change matplotlib backendd to "Agg"

[MichaMans]

Using the visuals function under linux leads to an Error:

ImportError: libGL.so.1: cannot open shared object file: No such file or directory

according to this issue the last comment recommend changing the matplotlib backend to "Agg".

I would change the Visuals class import to:

import matplotlib
matplotlib.use('Agg')

This should solve this