[FIX] Fixed rtd build

.readthedocs.yml

@@ -4,13 +4,16 @@
 
 # Required
 version: 2
+build:
+  os: ubuntu-20.04
+  tools:
+    python: "3.8"
 
 # 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: 3.8
   install:
     - requirements: docs/requirements.txt