Update README.md to latest version v1.5.2

Update README.md to latest version v1.5.2

README.md

@@ -18,7 +18,7 @@ learning to many products at Baidu.
 Our vision is to enable deep learning for everyone via PaddlePaddle.
 Please refer to our [release announcement](https://github.com/PaddlePaddle/Paddle/releases) to track the latest feature of PaddlePaddle.
 
-### Latest PaddlePaddle Release: [Fluid 1.5.1](https://github.com/PaddlePaddle/Paddle/tree/release/1.5)
+### Latest PaddlePaddle Release: [Fluid 1.5.2](https://github.com/PaddlePaddle/Paddle/tree/release/1.5)
 ### Install Latest Stable Release:
 ```
 # Linux CPU
@@ -26,9 +26,9 @@ pip install paddlepaddle
 # Linux GPU cuda10cudnn7
 pip install paddlepaddle-gpu
 # Linux GPU cuda8cudnn7
-pip install paddlepaddle-gpu==1.5.1.post87
+pip install paddlepaddle-gpu==1.5.2.post87
 # Linux GPU cuda9cudnn7
-pip install paddlepaddle-gpu==1.5.1.post97
+pip install paddlepaddle-gpu==1.5.2.post97
 
 
 # For installation on other platform, refer to http://paddlepaddle.org/