[DOC] fix syntax error for reference in plot_cost_complexity_pruning.py
@@ -14,7 +14,7 @@ increase the number of nodes pruned. Here we only show the effect of
``ccp_alpha`` on regularizing the trees and how to choose a ``ccp_alpha``
based on validation scores.
-See also `ref`:_minimal_cost_complexity_pruning` for details on pruning.
+See also :ref:`minimal_cost_complexity_pruning` for details on pruning.
"""
print(__doc__)
