Fixed a simple typo in cyvector.py
Fixed a simple typo in cyvector.py

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