Names (for classes, functions, variables etc) in Python can't start with a number

[yawor]

I've found in some recent change, that there's a class named 3DPrintingMaterials, which is an invalid Python name, as names can't start with a number:

STL-Volume-Model-Calculator/volume_calculator.py

Line 14 in ad57b78

class 3DPrintingMaterials:

[mcanet]

Yes, I fixed.