update mem_optim setting

python/paddle_serving_server_gpu/serve.py

@@ -34,7 +34,7 @@ def start_gpu_card_model(index, gpuid, args):  # pylint: disable=doc-string-miss
         port = args.port + index
     thread_num = args.thread
     model = args.model
-    mem_optim = args.mem_optim_off
+    mem_optim = args.mem_optim_off is False
     ir_optim = args.ir_optim
     max_body_size = args.max_body_size
     use_multilang = args.use_multilang