Update .readthedocs.yml

.readthedocs.yml

@@ -5,20 +5,21 @@
 # Required
 version: 2
 
+build:
+  os: "ubuntu-20.04"
+  tools:
+    python: "mambaforge-4.10"
+
 # Build documentation in the docs/ directory with Sphinx
 sphinx:
   configuration: docs/conf.py
 
-# Optionally build your docs in additional formats such as PDF and ePub
-formats: []
-
 # Install pyiron from conda 
 conda:
   environment: docs/environment.yml
 
 # Optionally set the version of Python and requirements required to build your docs
 python:
-  version: 3.7
   install:
     - method: pip
       path: .