change pip source, test=document_fix

doc/doc_ch/installation.md

@@ -52,11 +52,11 @@ hub.baidubce.com/paddlepaddle/paddle   latest-gpu-cuda9.0-cudnn7-dev    f56310dc
 pip3 install --upgrade pip
 
 如果您的机器安装的是CUDA9或CUDA10，请运行以下命令安装
-python3 -m pip install paddlepaddle-gpu==2.0.0b0 -i https://pypi.tuna.tsinghua.edu.cn/simple
+python3 -m pip install paddlepaddle-gpu==2.0.0b0 -i https://mirror.baidu.com/pypi/simple
 
 如果您的机器是CPU，请运行以下命令安装
 
-python3 -m pip install paddlepaddle==2.0.0b0 -i https://pypi.tuna.tsinghua.edu.cn/simple
+python3 -m pip install paddlepaddle==2.0.0b0 -i https://mirror.baidu.com/pypi/simple
 
 更多的版本需求，请参照[安装文档](https://www.paddlepaddle.org.cn/install/quick)中的说明进行操作。
 ```

doc/doc_en/installation_en.md

@@ -54,10 +54,10 @@ hub.baidubce.com/paddlepaddle/paddle   latest-gpu-cuda9.0-cudnn7-dev    f56310dc
 pip3 install --upgrade pip
 
 # If you have cuda9 or cuda10 installed on your machine, please run the following command to install
-python3 -m pip install paddlepaddle-gpu==2.0.0b0 -i https://pypi.tuna.tsinghua.edu.cn/simple
+python3 -m pip install paddlepaddle-gpu==2.0.0b0 -i https://mirror.baidu.com/pypi/simple
 
 # If you only have cpu on your machine, please run the following command to install
-python3 -m pip install paddlepaddle==2.0.0b0 -i https://pypi.tuna.tsinghua.edu.cn/simple
+python3 -m pip install paddlepaddle==2.0.0b0 -i https://mirror.baidu.com/pypi/simple
 ```
 For more software version requirements, please refer to the instructions in [Installation Document](https://www.paddlepaddle.org.cn/install/quick) for operation.