Update src/sage/combinat/abstract_tree.py

Co-authored-by: Travis Scrimshaw <clfrngrown@aol.com>

Author: fwjmath

src/sage/combinat/abstract_tree.py

@@ -2216,7 +2216,7 @@ def _require_mutable(self):
             ...
             ValueError: object is immutable; please change a copy instead.
 
-        EXAMPLES::
+        ::
 
             sage: T = LabelledRootedTree([]).clone()
             sage: T.node_number()