build(.readthedocs.yaml): Whoops, needed to add a build parameter.

Author: rbeyer

.readthedocs.yaml

@@ -5,6 +5,11 @@
 # Required
 version: 2
 
+build:
+  os: ubuntu-lts-latest
+  tools:
+    python: "3.9"
+
 # Build documentation in the docs/ directory with Sphinx
 sphinx:
   configuration: docs/conf.py
@@ -14,7 +19,6 @@ formats: all
 
 # Optionally set the version of Python and requirements required to build your docs
 python:
-  version: 3.9
   install:
     - requirements: docs/requirements.txt