Configure Cirrus CI (#9534)
Configure Cirrus CI (#9534)

Elixir is migrating from Travis to Cirrus CI to have a single
place to test against Unix, FreeBSD, and Windows.
elixir-lang/elixir,pedrosnk/elixir,kelvinst/elixir,joshprice/elixir,michalmuskala/elixir,ggcampinho/elixir,pedrosnk/elixir,ggcampinho/elixir,kimshrier/elixir,kimshrier/elixir,kelvinst/elixir