fix dead link in high_level_api.md

Author: luotao1

paddle/fluid/inference/api/high_level_api.md

@@ -57,4 +57,4 @@ By specifying the engine kind and config, one can get a specific implementation.
 ## Reference
 
 - [paddle_inference_api.h](./paddle_inference_api.h)
-- [some demos](./demo)
+- [some demos](./demo_ci)

paddle/fluid/inference/api/high_level_api_cn.md

@@ -83,5 +83,5 @@ CHECK(predictor->Run(slots, &outputs));
 
 ## 详细代码参考
 
-- [inference demos](./demo)
-- [复杂单线程/多线程例子](https://github.com/PaddlePaddle/Paddle/blob/develop/paddle/contrib/inference/test_paddle_inference_api_impl.cc)
+- [inference demos](./demo_ci)
+- [复杂单线程/多线程例子](https://github.com/PaddlePaddle/Paddle/blob/develop/paddle/fluid/inference/api/test_api_impl.cc)