fix doc

python/examples/faster_rcnn_model/README.md

@@ -13,7 +13,7 @@ If you want to have more detection models, please refer to [Paddle Detection Mod
 ```
 tar xf faster_rcnn_model.tar.gz
 mv faster_rcnn_model/pddet* .
-GLOG_v=2 python -m paddle_serving_server_gpu.serve --model pddet_serving_model --port 9494 --gpu_id 0
+GLOG_v=2 python -m paddle_serving_server_gpu.serve --model pddet_serving_model --port 9494 --gpu_ids 0
 ```
 
 ### Perform prediction

python/examples/faster_rcnn_model/README_CN.md

@@ -13,7 +13,7 @@ wget https://paddle-serving.bj.bcebos.com/pddet_demo/infer_cfg.yml
 ```
 tar xf faster_rcnn_model.tar.gz
 mv faster_rcnn_model/pddet* ./
-GLOG_v=2 python -m paddle_serving_server_gpu.serve --model pddet_serving_model --port 9494 --gpu_id 0
+GLOG_v=2 python -m paddle_serving_server_gpu.serve --model pddet_serving_model --port 9494 --gpu_ids 0
 ```
 
 ### 执行预测