message: Fix an error in cpp code.
  Change monster_generate.h to monster_generated.h
diff: @@ -370,7 +370,7 @@ The first step is to import/include the library, generated files, etc.
  <div class="language-cpp">
  ~~~{.cpp}
  - #include "monster_generate.h" // This was generated by `flatc`.
  + #include "monster_generated.h" // This was generated by `flatc`.
  using namespace MyGame::Sample; // Specified in the schema.
  ~~~
  