Fix broken link for sphinx-doc in generated docs (#5015)

Author: ryfi

Diff for: {{cookiecutter.project_slug}}/docs/howto.rst

@@ -26,7 +26,7 @@ Changes to files in `docs/_source` will be picked up and reloaded automatically.
 Docstrings to Documentation
 ----------------------------------------------------------------------
 
-The sphinx extension `apidoc <https://www.sphinx-doc.org/en/master/man/sphinx-apidoc.html/>`_ is used to automatically document code using signatures and docstrings.
+The sphinx extension `apidoc <https://www.sphinx-doc.org/en/master/man/sphinx-apidoc.html>`_ is used to automatically document code using signatures and docstrings.
 
 Numpy or Google style docstrings will be picked up from project files and available for documentation. See the `Napoleon <https://sphinxcontrib-napoleon.readthedocs.io/en/latest/>`_ extension for details.