fix bug in web_service

python/paddle_serving_server_gpu/web_service.py

@@ -221,6 +221,6 @@ class WebService(object):
         return feed, fetch
 
     def postprocess(self, feed=[], fetch=[], fetch_map=None):
-        for key in fetch_map.iterkeys():
+        for key in fetch_map:
             fetch_map[key] = fetch_map[key].tolist()
         return fetch_map