fix readthedocs build error
fix readthedocs build error

hirokihamasaki/irma,jbouyat/irma,jbouyat/irma,hirokihamasaki/irma,hirokihamasaki/irma,hirokihamasaki/irma,quarkslab/irma,quarkslab/irma,quarkslab/irma,quarkslab/irma,hirokihamasaki/irma,jbouyat/irma