Added serial host back to travis
Added serial host back to travis

aliafshar/firebase-arduino,FirebaseExtended/firebase-arduino,aliafshar/firebase-arduino,aliafshar/firebase-arduino,ed7coyne/firebase-arduino,FirebaseExtended/firebase-arduino,gguuss/firebase-arduino,gguuss/firebase-arduino,FirebaseExtended/firebase-arduino,gguuss/firebase-arduino