Updating readthedocs for build.os

Change-Id: Idab356fde2b98f1b1cbc24e8132126de6cb02704
Signed-off-by: czichy <thoralf.czichy@nokia.com>
diff --git a/.readthedocs.yaml b/.readthedocs.yaml
index 3797dc8..243587e 100644
--- a/.readthedocs.yaml
+++ b/.readthedocs.yaml
@@ -9,10 +9,11 @@
   - htmlzip
 
 build:
-  image: latest
+  os: latest
+  tools:
+    python: "3.7"
 
 python:
-  version: 3.7
   install:
     - requirements: docs/requirements-docs.txt