CI: fix a Travis issue with python3
CI: fix a Travis issue with python3

dominicgs/GreatFET-experimental,greatscottgadgets/greatfet,greatscottgadgets/greatfet,dominicgs/GreatFET-experimental,greatscottgadgets/greatfet,dominicgs/GreatFET-experimental,greatscottgadgets/greatfet