Chapter 18: env.render() fails on Ubuntu 18.04

I am hitting this issue on a VM running in the Azure cloud:

```bash
(tf2) mingqxu@rl:~/handson-ml2$ uname -a
Linux rl 5.0.0-1027-azure #29~18.04.1-Ubuntu SMP Mon Nov 25 21:18:57 UTC 2019 x86_64 x86_64 x86_64 GNU/Linux

(tf2) mingqxu@rl:~/handson-ml2$ cat render.py
```

```python
import gym

env = gym.make('CartPole-v1')
env.seed(42)
obs = env.reset()
try:
import pyvirtualdisplay
display = pyvirtualdisplay.Display(visible=0, size=(1400, 900)).start()
except ImportError:
pass

env.render()
env.close()
```

```bash
(tf2) mingqxu@rl:~/handson-ml2$ python render.py
```

```python
xdpyinfo was not found, X start can not be checked! Please install xdpyinfo!
Traceback (most recent call last):
File "render.py", line 12, in
env.render()
File "/home/mingqxu/anaconda3/envs/tf2/lib/python3.7/site-packages/gym/core.py", line 235, in render
return self.env.render(mode, **kwargs)
File "/home/mingqxu/anaconda3/envs/tf2/lib/python3.7/site-packages/gym/envs/classic_control/cartpole.py", line 150, in render
from gym.envs.classic_control import rendering
File "/home/mingqxu/anaconda3/envs/tf2/lib/python3.7/site-packages/gym/envs/classic_control/rendering.py", line 27, in
from pyglet.gl import *
File "/home/mingqxu/anaconda3/envs/tf2/lib/python3.7/site-packages/pyglet/gl/__init__.py", line 221, in
from .xlib import XlibConfig as Config
File "/home/mingqxu/anaconda3/envs/tf2/lib/python3.7/site-packages/pyglet/gl/xlib.py", line 12, in
from pyglet.canvas.xlib import XlibCanvas
File "/home/mingqxu/anaconda3/envs/tf2/lib/python3.7/site-packages/pyglet/canvas/__init__.py", line 103, in
from pyglet.canvas.xlib import XlibDisplay as Display
File "/home/mingqxu/anaconda3/envs/tf2/lib/python3.7/site-packages/pyglet/canvas/xlib.py", line 19, in
from . import xlib_vidmoderestore
File "/home/mingqxu/anaconda3/envs/tf2/lib/python3.7/site-packages/pyglet/canvas/xlib_vidmoderestore.py", line 23, in
from pyglet.libs.x11 import xlib
File "/home/mingqxu/anaconda3/envs/tf2/lib/python3.7/site-packages/pyglet/libs/x11/xlib.py", line 2928, in
XEHeadOfExtensionList.argtypes = [XEDataObject]
TypeError: item 1 in _argtypes_ passes a union by value, which is unsupported.
```