build.sh: Fix update-boot-image help
build.sh: Fix update-boot-image help

mrjbq7/factor,tgunr/factor,mrjbq7/factor,bpollack/factor,tgunr/factor,bpollack/factor,factor/factor,bpollack/factor,factor/factor,tgunr/factor,bpollack/factor,factor/factor,mrjbq7/factor,tgunr/factor,factor/factor,mrjbq7/factor,mrjbq7/factor,factor/factor,factor/factor,tgunr/factor,bpollack/factor,mrjbq7/factor,tgunr/factor,bpollack/factor,bpollack/factor