Fix sklearn docs throwing an error during build (#214)

Author: Yard1

xgboost_ray/sklearn.py

@@ -214,7 +214,8 @@ def _treat_estimator_doc(doc: str) -> str:
     """Helper function to make nececssary changes in estimator docstrings"""
     doc = doc.replace(*_N_JOBS_DOC_REPLACE).replace(
         "scikit-learn API for XGBoost",
-        "scikit-learn API for Ray-distributed XGBoost")
+        "scikit-learn API for Ray-distributed XGBoost").replace(
+            ":doc:`tree method\n        </treemethod>`", "tree method")
     return doc