[Travis] Attempt to fix build #2

celery/backends/base.py

@@ -581,7 +581,7 @@ class BaseKeyValueStoreBackend(Backend):
                       traceback=None, request=None, **kwargs):
         meta = {'status': state, 'result': result, 'traceback': traceback,
                 'children': self.current_task_children(request),
-                'task_id': task_id}
+                'task_id': bytes_to_str(task_id)}
         self.set(self.get_key_for_task(task_id), self.encode(meta))
         return result