Fixes "Error parsing json: -1" error

Buzzing the RL78 was consistently giving JSON parsing errors
due to the length of the message arriving to the board.

The issue was that we were allocating too few JSMN tokens
to properly parse the beep message coming from the UI.

Descriptions of the JSMN errors can be consulted at:

https://github.com/buglabs/bugswarm-renesas/blob/renesas_factory_release/jsmn/jsmn.h#L18-L27