Fix doc string

docs/tutorials/advanced/classification_of_strategies.rst

@@ -101,7 +101,7 @@ Some strategies have been classified as having a particularly long run time::
     ... }
     >>> strategies = axl.filtered_strategies(filterset)
     >>> len(strategies)
-    10
+    11
 
 Strategies that :code:`manipulate_source`, :code:`manipulate_state`
 and/or :code:`inspect_source` return :code:`False` for the :code:`obey_axelrod`