DOC: Fixed reference (pandas-dev#24470)

[ci skip]

Author: TomAugspurger

pandas/core/series.py

@@ -437,7 +437,7 @@ def values(self):
         .. warning::
 
            We recommend using :attr:`Series.array` or
-           :Series:`Index.to_numpy`, depending on whether you need
+           :meth:`Series.to_numpy`, depending on whether you need
            a reference to the underlying data or a NumPy array.
 
         Returns