SyntaxWarning for cartesianPlotFunction2D.py

[Berserker2251]

In line 264 column 26 of cartesianPlotFunction2D.py there's a SyntaxWarning for the text "\pi " when executed in inkscape with the extension active, which could be fixed using "\\pi " or r"\pi " for which the one after I didn't attempt to test. Not sure whether it's affecting LaTeX rendering but I fixed it from the get go.

Hope this helps.