Update scikit version

Author: raydouglass

conda/recipes/nightly-versions.yaml

@@ -80,6 +80,6 @@ protobuf_version:
 rapidjson_version:
   - '=1.1.0'
 scikit_learn_version:
-  - '=0.21.3'
+  - '=0.23.1'
 scipy_version:
   - '=1.3.0'