message: fix quickstart fit_a_line path
diff: @@ -8,7 +8,7 @@ This quick start example is mainly for those users who already have a model to d
  get into the Serving git directory, and change dir to `fit_a_line`
  ``` shell
  -cd Serving/python/examples/fit_a_line
  +cd Serving/examples/C++//fit_a_line
  sh get_data.sh
  ```
  