Fix for the #539 classic build fails when VS 2017 installed.
Fix for the #539 classic build fails when VS 2017 installed.

dmitriyse/pythonnet,AlexCatarino/pythonnet,yagweb/pythonnet,AlexCatarino/pythonnet,dmitriyse/pythonnet,pythonnet/pythonnet,AlexCatarino/pythonnet,pythonnet/pythonnet,pythonnet/pythonnet,AlexCatarino/pythonnet,yagweb/pythonnet,dmitriyse/pythonnet,QuantConnect/pythonnet,QuantConnect/pythonnet,yagweb/pythonnet,yagweb/pythonnet,QuantConnect/pythonnet