Polish doc style

doc/fluid/advanced_usage/development/contribute_to_paddle.md

@@ -92,8 +92,9 @@ no changes added to commit (use "git add" and/or "git commit -a")
 ➜  docker run -v $(pwd):/paddle -e "WITH_GPU=OFF" -e "WITH_AVX=ON" -e "WITH_TESTING=ON" paddle:latest-dev
 ```
 
- 如果你需要在此基础上编译基于Python3的PaddlePaddle，可以：
- ```bash
+如果你需要在此基础上编译基于Python3的PaddlePaddle，可以：
+
+```bash
 ➜  docker run -v $(pwd):/paddle -e "PY_VERSION=3.5" -e "WITH_FLUID_ONLY=ON" -e "WITH_GPU=OFF" -e "WITH_AVX=ON" -e "WITH_TESTING=ON" paddle:latest-dev
 ```