Require the latest versions of Sphinx.

HexDecimal · HexDecimal · commit 5934413481d4 · 2021-10-19T21:21:39.000-07:00
So that RTD uses a version later than Sphinx 1.
diff --git a/.readthedocs.yml b/.readthedocs.yml
@@ -18,7 +18,7 @@ formats:
   - epub
 
 python:
-  version: 3.8
+  version: "3.8"
   install:
-  - requirements: requirements.txt
-  - requirements: docs/requirements.txt
+    - requirements: requirements.txt
+    - requirements: docs/requirements.txt
diff --git a/docs/requirements.txt b/docs/requirements.txt
@@ -1 +1,2 @@
+sphinx>=4.2
 sphinx_rtd_theme
