Build python 3 before python 2 on appveyor
Build python 3 before python 2 on appveyor

mwcraig/vpython-jupyter,BruceSherwood/vpython-jupyter,mwcraig/vpython-jupyter,BruceSherwood/vpython-jupyter,mwcraig/vpython-jupyter,BruceSherwood/vpython-jupyter,BruceSherwood/vpython-jupyter,mwcraig/vpython-jupyter