fix typo. give self._configuration instead of configuration

pypushflow/Workflow.py

@@ -44,7 +44,8 @@ class _BaseWorkflow:
         self._add_ons = []
         for add_on_class in self._getAddOnsClasses():
             self._add_ons.append(add_on_class(workflow=self,
-                                              configuration=configuration))
+                                              configuration=self._configuration
+                                              ))
 
     def _getAddOnsClasses(self):
         add_ons = []