Fix readthedocs build error (morphocut#112)

See readthedocs/readthedocs.org#10290

.readthedocs.yml

@@ -5,13 +5,18 @@
 # Required
 version: 2
 
+# Configure build environment
+build:
+  os: ubuntu-22.04
+  tools:
+    python: "3.10"
+
 # Build documentation in the docs/ directory with Sphinx
 sphinx:
   configuration: docs/conf.py
 
 # Optionally set the version of Python and requirements required to build your docs
 python:
-  version: 3.7
   install:
     - method: pip
       path: .