The declaration of the flush function is obsolete

[xiong-frank]

The flush function in the example is defined as follows:

    static void cb_stdout_flush(const void *data, size_t bytes,
                            const char *tag, int tag_len,
                            struct flb_input_instance *i_ins,
                            void *out_context,
                            struct flb_config *config)

But in the latest flunt-bit source code, the declaration of the flush function is:
https://github.com/fluent/fluent-bit/blob/master/include/fluent-bit/flb_output.h#L196

    void (*cb_flush) (struct flb_event_chunk *,
                      struct flb_output_flush *,
                      struct flb_input_instance *,
                      void *,
                      struct flb_config *);

the function definitions in the examples need to be updated to avoid ambiguity for plugin developers.