Making an object visible causes an error in javascript

[mwcraig]

With the release 7.5.0beta2 the following code fails:

from vpython import *
s = sphere()
s.visible = False

The sphere isn't turned invisible, and the javascript console gives this error:

(index):925 Uncaught TypeError: Cannot set property 'vs' of undefined
    at handle_attrs ((index):925)
    at handler ((index):514)
    at WebSocket.ws.onmessage ((index):74)

The line on which it fails is https://github.com/BruceSherwood/vpython-jupyter/blob/master/vpython/vpython_libraries/glowcomm.html#L925, added in https://github.com/BruceSherwood/vpython-jupyter/pull/126

Not sure how to fix it but am hoping the fix isn't too messy 😀

[mwcraig]

Closed by #132