README: testcase_func_name -> name_func

`testcase_func_name` was deprecated in favor of `name_func`, but README still references the former, which we correct here.
diff --git a/README.rst b/README.rst
index 9014bc1..6b839d1 100644
--- a/README.rst
+++ b/README.rst
@@ -353,7 +353,7 @@
 ``test_add_0_2_and_3`` and ``test_add_1_3_and_5``.
 
 The names of the test cases generated by ``@parameterized.expand`` can be
-customized using the ``testcase_func_name`` keyword argument. The value should
+customized using the ``name_func`` keyword argument. The value should
 be a function which accepts three arguments: ``testcase_func``, ``param_num``,
 and ``params``, and it should return the name of the test case.
 ``testcase_func`` will be the function to be tested, ``param_num`` will be the
@@ -375,7 +375,7 @@
         @parameterized.expand([
             (2, 3, 5),
             (2, 3, 5),
-        ], testcase_func_name=custom_name_func)
+        ], name_func=custom_name_func)
         def test_add(self, a, b, expected):
             assert_equal(a + b, expected)