Update dependency Sphinx to v4 (#643)

renovate[bot] · web-flow · commit fe61770ae0df · 2021-05-10T14:35:52.000+03:00
diff --git a/requirements-doc.txt b/requirements-doc.txt
@@ -1,2 +1,2 @@
-Sphinx==3.5.4
+Sphinx==4.0.0
 sphinx-rtd-theme==0.5.2
