fix doc

doc/LOW_PRECISION_DEPLOYMENT.md

@@ -17,7 +17,7 @@ python -m paddle_serving_client.convert --dirname ResNet50_quant
 ```
 Start RPC service, specify the GPU id and precision mode
 ```
-python -m paddle_serving_server.serve --model serving_server --port 9393 --gpu_ids 0 --use_gpu --use_trt --precision int8 
+python -m paddle_serving_server.serve --model serving_server --port 9393 --gpu_ids 0 --use_trt --precision int8 
 ```
 Request the serving service with Client
 ```

doc/LOW_PRECISION_DEPLOYMENT_CN.md

@@ -16,7 +16,7 @@ python -m paddle_serving_client.convert --dirname ResNet50_quant
 ```
 启动rpc服务, 设定所选GPU id、部署模型精度
 ```
-python -m paddle_serving_server.serve --model serving_server --port 9393 --gpu_ids 0 --use_gpu --use_trt --precision int8 
+python -m paddle_serving_server.serve --model serving_server --port 9393 --gpu_ids 0 --use_trt --precision int8 
 ```
 使用client进行请求
 ```