dask: add missing self argument

Author: alvarolopez

deepaas/model/v2/executor.py

@@ -73,5 +73,5 @@ def submit(self, fn, *args, **kwargs):
         fut = self.client.submit(fn, *args, **kwargs)
         return fut
 
-    def shutdown():
+    def shutdown(self):
         self.client.shutdown()