Fix ReadTheDocs Build Errors

# Situation



ReadTheDocs.org gives us some strange errors:



```

Requirement already satisfied: pytz>=2015.7 in /home/docs/checkouts/readthedocs.org/user_builds/python-semver/envs/latest/lib/python3.7/site-packages (from babel!=2.0,>=1.3->sphinx->-r docs/requirements.txt (line 2)) (2020.1)

Collecting sphinxcontrib-htmlhelp

  Downloading sphinxcontrib_htmlhelp-1.0.3-py2.py3-none-any.whl (96 kB)

Collecting sphinxcontrib-applehelp

  Downloading sphinxcontrib_applehelp-1.0.2-py2.py3-none-any.whl (121 kB)

Collecting sphinxcontrib-jsmath

  Downloading sphinxcontrib_jsmath-1.0.1-py2.py3-none-any.whl (5.1 kB)

Collecting sphinxcontrib-devhelp

  Downloading sphinxcontrib_devhelp-1.0.2-py2.py3-none-any.whl (84 kB)

Collecting sphinxcontrib-qthelp

  Downloading sphinxcontrib_qthelp-1.0.3-py2.py3-none-any.whl (90 kB)

Building wheels for collected packages: sphinx-argparse

  Building wheel for sphinx-argparse (setup.py): started

  Building wheel for sphinx-argparse (setup.py): finished with status 'done'

  Created wheel for sphinx-argparse: filename=sphinx_argparse-0.2.5-py3-none-any.whl size=11549 sha256=a6cd6938c3c655193f230e0181f48d037539475be6989b7f17d59760167f5c54

  Stored in directory: /tmp/pip-ephem-wheel-cache-s8zdxc9_/wheels/4a/4c/12/83c88bdc1bc352d7036de2891b5d6729adcf1bda3bab015560

Successfully built sphinx-argparse

ERROR: Exception:

Traceback (most recent call last):

  File "/home/docs/checkouts/readthedocs.org/user_builds/python-semver/envs/latest/lib/python3.7/site-packages/pip/_internal/cli/base_command.py", line 228, in _main

    status = self.run(options, args)

  File "/home/docs/checkouts/readthedocs.org/user_builds/python-semver/envs/latest/lib/python3.7/site-packages/pip/_internal/cli/req_command.py", line 182, in wrapper

    return func(self, options, args)

  File "/home/docs/checkouts/readthedocs.org/user_builds/python-semver/envs/latest/lib/python3.7/site-packages/pip/_internal/commands/install.py", line 379, in run

    requirement_set

  File "/home/docs/checkouts/readthedocs.org/user_builds/python-semver/envs/latest/lib/python3.7/site-packages/pip/_internal/resolution/resolvelib/resolver.py", line 191, in get_installation_order

    weights = get_topological_weights(graph)

  File "/home/docs/checkouts/readthedocs.org/user_builds/python-semver/envs/latest/lib/python3.7/site-packages/pip/_internal/resolution/resolvelib/resolver.py", line 242, in get_topological_weights

    assert len(weights) == len(graph)

AssertionError

```



# Suggested Solution



Fix the problem.



@tlaferriere Thomas, do you know what can be the problem?

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