Google Colab notebook example does not work

[niranjantdesai]

I got the following error when I was trying to run the example in the Google Colab notebook:

---------------------------------------------------------------------------
NoSuchDisplayException                    Traceback (most recent call last)
[<ipython-input-1-10b668dbca31>](https://localhost:8080/#) in <module>()
    138 
    139 cam_node = scene.add(cam, pose=cam_pose)
--> 140 r = OffscreenRenderer(viewport_width=640*2, viewport_height=480*2)
    141 color, depth = r.render(scene)
    142 r.delete()

6 frames
[/usr/local/lib/python3.7/dist-packages/pyglet/canvas/xlib.py](https://localhost:8080/#) in __init__(self, name, x_screen)
    121         self._display = xlib.XOpenDisplay(name)
    122         if not self._display:
--> 123             raise NoSuchDisplayException('Cannot connect to "%s"' % name)
    124 
    125         screen_count = xlib.XScreenCount(self._display)

NoSuchDisplayException: Cannot connect to "None"

The output of print(gl.glGetString(gl.GL_VERSION)) and print(gl.glGetString(gl.GL_VENDOR)) is None.

This happened with both GPU and TPU runtimes.