.travis: Delete old rubygems after we install it.
.travis: Delete old rubygems after we install it.

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