add sphinx configuration to readthedocs.yml

.readthedocs.yml

@@ -1,6 +1,9 @@
 # This is the version for the readthedocs configuration. Version 2 ignores
 # web-based configuration and uses everything from this file.
 version: 2
+sphinx:
+  configuration: docs/source/conf.py
+  fail_on_warning: true
 
 # Configure the python version and environment construction run before
 # docs are built.
@@ -16,6 +19,3 @@ python:
       extra_requirements:
         - docs
 
-# Doc builds will fail if there are any warnings
-sphinx:
-  fail_on_warning: true