Follow comments.

doc/design/multi_language_interface/00.why_plain_c.md

@@ -58,14 +58,14 @@ typedef void* paddle_matrix;
 typedef int paddle_error;
 
 extern "C"
-paddle_error paddle_matrix_shape(paddle_matrix matrix,
-                                 uint64_t* width,
-                                 uint64_t* height);
+paddle_error paddle_matrix_get_shape(paddle_matrix matrix,
+                                     uint64_t* width,
+                                     uint64_t* height);
 ```
 而在CPP里面实现这个C的接口，文件 `paddle_matrix.cpp`
 
 ```cpp
-#include "paddle/math/matrix.hpp"
+#include "paddle/math/matrix.h"
 extern "C"
 paddle_error paddle_matrix_shape(paddle_matrix matrix,
                                  uint64_t *width,