markdown.extensions Module is Missing

Steps to reproduce

• Run pip install gitbuilding
• Run gitbuilding serve
• Access http://localhost:6178/ from a web browser
• Review the stack trace in the console window

What happened?

I installed and ran GitBuilding 0.11.0 according to the instructions on the website. There were no errors when GitBuilding started up. However, when I try to access the server URL from a browser, I get the following stack trace. The main error is ModuleNotFoundError: No module named 'markdown.extensions.md_in_html' Is there a dependency missing from the setup configuration?

$ gitbuilding serve
GitBuilding server running on http://localhost:6178/ (Press CTRL+C to quit)
ERROR:gitbuilding.server:Exception on / [GET]
Traceback (most recent call last):
  File "/home/jwright/.local/lib/python3.8/site-packages/flask/app.py", line 2073, in wsgi_app
    response = self.full_dispatch_request()
  File "/home/jwright/.local/lib/python3.8/site-packages/flask/app.py", line 1518, in full_dispatch_request
    rv = self.handle_user_exception(e)
  File "/home/jwright/.local/lib/python3.8/site-packages/flask/app.py", line 1516, in full_dispatch_request
    rv = self.dispatch_request()
  File "/home/jwright/.local/lib/python3.8/site-packages/flask/app.py", line 1502, in dispatch_request
    return self.ensure_sync(self.view_functions[rule.endpoint])(**req.view_args)
  File "/home/jwright/.local/lib/python3.8/site-packages/gitbuilding/server.py", line 559, in _render_page
    return self._render_markdown_page(path)
  File "/home/jwright/.local/lib/python3.8/site-packages/gitbuilding/server.py", line 571, in _render_markdown_page
    return self.renderer.render_md(path.gb_file.content,
  File "/home/jwright/.local/lib/python3.8/site-packages/gitbuilding/render.py", line 383, in render_md
    content_html = markdown(md,
  File "/usr/lib/python3/dist-packages/markdown/core.py", line 390, in markdown
    md = Markdown(**kwargs)
  File "/usr/lib/python3/dist-packages/markdown/core.py", line 99, in __init__
    self.registerExtensions(extensions=kwargs.get('extensions', []),
  File "/usr/lib/python3/dist-packages/markdown/core.py", line 126, in registerExtensions
    ext = self.build_extension(ext, configs.get(ext, {}))
  File "/usr/lib/python3/dist-packages/markdown/core.py", line 166, in build_extension
    module = importlib.import_module(ext_name)
  File "/usr/lib/python3.8/importlib/__init__.py", line 127, in import_module
    return _bootstrap._gcd_import(name[level:], package, level)
  File "<frozen importlib._bootstrap>", line 1014, in _gcd_import
  File "<frozen importlib._bootstrap>", line 991, in _find_and_load
  File "<frozen importlib._bootstrap>", line 973, in _find_and_load_unlocked
ModuleNotFoundError: No module named 'markdown.extensions.md_in_html'

What should have happened?

• The GitBuilding web interface should have loaded, but I get an Internal Server Error message in the browser instead.

Version/OS/Installation method

• Version: 0.11.0
• Operating System: Ubuntu 20.04 64-bit
• Installation source: pip install gitbuilding