travis: add osx build
travis: add osx build

(cherry picked from commit 81061ffd694958383496a4d1e628d764e648ffbe)

reddcoin-project/reddcoin,reddcoin-project/reddcoin,reddcoin-project/reddcoin,reddcoin-project/reddcoin,reddcoin-project/reddcoin,reddcoin-project/reddcoin