message: modify v0.8.0 doc
diff: @@ -66,7 +66,6 @@ pip3 install -r python/requirements.txt
  ```shell
  pip3 install paddle-serving-client==0.8.0 -i https://pypi.tuna.tsinghua.edu.cn/simple
  -
  pip3 install paddle-serving-app==0.8.0 -i https://pypi.tuna.tsinghua.edu.cn/simple
  # CPU Server
  