.travis.yml: try and use addons/homebrew.
.travis.yml: try and use addons/homebrew.

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