Update apiref.rst
fix the documentation about json_dumps. refs
@@ -1091,7 +1091,9 @@ These functions output UTF-8:
Returns the JSON representation of *json* as a string, or *NULL* on
error. *flags* is described above. The return value must be freed
- by the caller using :func:`free()`.
+ by the caller using :func:`free()`. Note that if you have called
+ :func:`json_set_alloc_funcs()` to override :func:`free()`, you should
+ call your custom free function instead to free the return value.
.. function:: size_t json_dumpb(const json_t *json, char *buffer, size_t size, size_t flags)
