Set "sphinx" 3.1.2 as the maximum usable version.
@@ -67,7 +67,7 @@ pre-commit = { version = "*", optional = true } # Development dependency.
pygraphviz = { version = "*", optional = true }
pytest = { version = "*", optional = true } # Development dependency.
restructuredtext-lint = { version = "*", optional = true } # Development dependency.
-sphinx = { version = "*", optional = true } # Development dependency.
+sphinx = { version = "<=3.1.2", optional = true } # Development dependency.
sphinx_rtd_theme = { version = "*", optional = true } # Development dependency.
sphinxcontrib-bibtex = { version = "*", optional = true } # Development dependency.
toml = { version = "*", optional = true } # Development dependency.
@@ -88,7 +88,7 @@ nose = "*"
pre-commit = "*"
pytest = "*"
restructuredtext-lint = "*"
-sphinx = "*"
+sphinx = "<=3.1.2"
sphinx_rtd_theme = "*"
sphinxcontrib-bibtex = "*"
toml = "*"
