AttributeError: module 'typing' has no attribute '_ClassVar'

### Describe the error
Hi. I am facing this issue of dataclass while running the example scene. Any ideas on how to resolve them?

### Code and Error
**Code**:
manim-render example_scenes.py OpeningManimExample
**Error**:
Traceback (most recent call last):
File "c:\users\\.conda\envs\masters\lib\runpy.py", line 194, in _run_module_as_main
return _run_code(code, main_globals, None,
File "c:\users\\.conda\envs\masters\lib\runpy.py", line 87, in _run_code
exec(code, run_globals)
File "C:\Users\\.conda\envs\masters\Scripts\manim-render.exe\__main__.py", line 4, in
File "c:\users\\.conda\envs\masters\lib\site-packages\manimlib\__init__.py", line 3, in
from manimlib.animation.animation import *
File "c:\users\\.conda\envs\masters\lib\site-packages\manimlib\animation\animation.py", line 3, in
from manimlib.mobject.mobject import _AnimationBuilder
File "c:\users\\.conda\envs\masters\lib\site-packages\manimlib\mobject\mobject.py", line 29, in
from manimlib.shader_wrapper import ShaderWrapper
File "c:\users\\.conda\envs\masters\lib\site-packages\manimlib\shader_wrapper.py", line 7, in
from manimlib.utils.directories import get_shader_dir
File "c:\users\\.conda\envs\masters\lib\site-packages\manimlib\utils\directories.py", line 4, in
from manimlib.utils.customization import get_customization
File "c:\users\\.conda\envs\masters\lib\site-packages\manimlib\utils\customization.py", line 4, in
from manimlib.config import get_custom_config
File "c:\users\\.conda\envs\masters\lib\site-packages\manimlib\config.py", line 8, in
from screeninfo import get_monitors
File "c:\users\\.conda\envs\masters\lib\site-packages\screeninfo\__init__.py", line 1, in
from .common import Enumerator, Monitor
File "c:\users\\.conda\envs\masters\lib\site-packages\screeninfo\common.py", line 7, in
class Monitor:
File "C:\ProgramData\Anaconda3\Lib\site-packages\dataclasses.py", line 958, in dataclass
return wrap(_cls)
File "C:\ProgramData\Anaconda3\Lib\site-packages\dataclasses.py", line 950, in wrap
return _process_class(cls, init, repr, eq, order, unsafe_hash, frozen)
File "C:\ProgramData\Anaconda3\Lib\site-packages\dataclasses.py", line 800, in _process_class
cls_fields = [_get_field(cls, name, type)
File "C:\ProgramData\Anaconda3\Lib\site-packages\dataclasses.py", line 800, in
cls_fields = [_get_field(cls, name, type)
File "C:\ProgramData\Anaconda3\Lib\site-packages\dataclasses.py", line 659, in _get_field
if (_is_classvar(a_type, typing)
File "C:\ProgramData\Anaconda3\Lib\site-packages\dataclasses.py", line 550, in _is_classvar
return type(a_type) is typing._ClassVar
AttributeError: module 'typing' has no attribute '_ClassVar'
### Environment
**OS System**: Windows Anaconda
**manim version**:

Name: manimgl
Version: 1.0.0
Summary: Animation engine for explanatory math videos
Home-page: https://github.com/3b1b/manim
Author: Grant Sanderson
Author-email: grant@3blue1brown.com
License: MIT
Location: c:\users\afarooqui\.conda\envs\masters\lib\site-packages
Requires: screeninfo, argparse, pyyaml, validators, moderngl-window, pyreadline, Pillow, scipy, progressbar, tqdm, mapbox-earcut, pydub, matplotlib, ipython, moderngl, colour, manimpango, sympy, PyOpenGL, numpy
Required-by:

**python version**: 3.8