pyglet.gl.ContextException: Could not create GL context

I try installing manima as follows :
```
# Install python requirements
pip install -r requirements.txt

# Try it out
python manim.py example_scenes.py OpeningManimExample
```
However, following errors occured.
How can I fix this ?

```
Traceback (most recent call last):
File "manim.py", line 5, in
manimlib.main()
File "/home/maru/manim/manimlib/__init__.py", line 9, in main
scenes = manimlib.extract_scene.main(config)
File "/home/maru/manim/manimlib/extract_scene.py", line 113, in main
scenes = get_scenes_to_render(all_scene_classes, scene_config, config)
File "/home/maru/manim/manimlib/extract_scene.py", line 74, in get_scenes_to_render
scene = scene_class(**scene_config)
File "/home/maru/manim/manimlib/scene/scene.py", line 46, in __init__
self.window = Window(self, **self.window_config)
File "/home/maru/manim/manimlib/window.py", line 20, in __init__
super().__init__(**kwargs)
File "/home/maru/.local/lib/python3.8/site-packages/moderngl_window/context/pyglet/window.py", line 51, in __init__
self._window = PygletWrapper(
File "/home/maru/.local/lib/python3.8/site-packages/pyglet/window/xlib/__init__.py", line 173, in __init__
super(XlibWindow, self).__init__(*args, **kwargs)
File "/home/maru/.local/lib/python3.8/site-packages/pyglet/window/__init__.py", line 606, in __init__
context = config.create_context(gl.current_context)
File "/home/maru/.local/lib/python3.8/site-packages/pyglet/gl/xlib.py", line 204, in create_context
return XlibContextARB(self, share)
File "/home/maru/.local/lib/python3.8/site-packages/pyglet/gl/xlib.py", line 314, in __init__
super(XlibContext13, self).__init__(config, share)
File "/home/maru/.local/lib/python3.8/site-packages/pyglet/gl/xlib.py", line 218, in __init__
raise gl.ContextException('Could not create GL context')
pyglet.gl.ContextException: Could not create GL context

```