Fix deprecated link to Python Testing Tools Taxonomy. Reported by Daniel Greenfeld on docs@.

Doc/library/unittest.rst

@@ -91,7 +91,7 @@ need to derive from a specific class.
       Third-party unittest frameworks with a lighter-weight syntax for writing
       tests.  For example, ``assert func(10) == 42``.
 
-   `The Python Testing Tools Taxonomy <http://pycheesecake.org/wiki/PythonTestingToolsTaxonomy>`_
+   `The Python Testing Tools Taxonomy <http://wiki.python.org/moin/PythonTestingToolsTaxonomy>`_
       An extensive list of Python testing tools including functional testing
       frameworks and mock object libraries.