update comment

python/examples/ocr/README.md

@@ -26,7 +26,7 @@ tar xf test_imgs.tar
 python -m paddle_serving_server.serve --model ocr_det_model --port 9293
 python ocr_web_server.py cpu
 #for gpu user
-python -m paddle_serving_server.serve --model ocr_det_model --port 9293 --gpu_id 0
+python -m paddle_serving_server.serve --model ocr_det_model --port 9293 --gpu_ids 0
 python ocr_web_server.py gpu
 ```
 
@@ -111,7 +111,7 @@ After the -- model parameter, the folder path of multiple model files is passed
 #for cpu user
 python -m paddle_serving_server.serve --model ocr_det_model ocr_rec_model --port 9293
 #for gpu user
-python -m paddle_serving_server.serve --model ocr_det_model ocr_rec_model --port 9293 --gpu_id 0
+python -m paddle_serving_server.serve --model ocr_det_model ocr_rec_model --port 9293 --gpu_ids 0
 ```
 
 ### Client Prediction