update .travis.yml to test on osx (#5740)
update .travis.yml to test on osx (#5740)


lexmag/elixir,kimshrier/elixir,ggcampinho/elixir,pedrosnk/elixir,beedub/elixir,lexmag/elixir,antipax/elixir,kimshrier/elixir,gfvcastro/elixir,pedrosnk/elixir,kelvinst/elixir,kelvinst/elixir,michalmuskala/elixir,ggcampinho/elixir,elixir-lang/elixir,gfvcastro/elixir,joshprice/elixir,beedub/elixir,antipax/elixir