Update decisiontrees.rst

Fixed reference indent level

Author: b-sherman

docs/source/content/supervised/decisiontrees.rst

@@ -318,9 +318,8 @@ whether Mike will go shopping:
     prediction_results = tree.predict(encoder.transform(prediction_data))
 
 
-************
 References
-************
+----------
 
 1. https://towardsdatascience.com/decision-trees-in-machine-learning-641b9c4e8052
 2. https://heartbeat.fritz.ai/introduction-to-decision-tree-learning-cd604f85e23