travis: drop OSX environment (#920)
travis: drop OSX environment (#920)


Martin2112/trillian,Martin2112/trillian,codingllama/trillian,daviddrysdale/trillian,RJPercival/trillian,codingllama/trillian,Martin2112/trillian,daviddrysdale/trillian,gdbelvin/trillian,RJPercival/trillian,daviddrysdale/trillian,google/trillian,google/trillian,AlCutter/trillian,gdbelvin/trillian,gdbelvin/trillian,AlCutter/trillian