fix quickstart fit_a_line path

doc/Quick_Start_CN.md

@@ -8,7 +8,7 @@
 
 进入到Serving的git目录下，进入到`fit_a_line`例子
 ``` shell
-cd Serving/python/examples/fit_a_line
+cd Serving/examples/C++//fit_a_line
 sh get_data.sh
 ```
 

doc/Quick_Start_EN.md

@@ -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
 ```