DOC: Update link in the deprecation message for .ix

Author: Chris Kerr <chris.kerr@athion.de>

Closes #16691 from frexvahi/update-ix-deprecated-link and squashes the following commits:

1c44ba6 [Chris Kerr] Update link in the deprecation message for .ix

(cherry picked from commit 6401b82)

pandas/core/indexing.py

@@ -1288,7 +1288,7 @@ def __init__(self, obj, name):
 .iloc for positional indexing
 
 See the documentation here:
-http://pandas.pydata.org/pandas-docs/stable/indexing.html#deprecate_ix"""
+http://pandas.pydata.org/pandas-docs/stable/indexing.html#ix-indexer-is-deprecated"""  # noqa
 
         warnings.warn(_ix_deprecation_warning,
                       DeprecationWarning, stacklevel=3)