Fix error message for missing GreatFET
Fix error message for missing GreatFET

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