Configure Travis to test both nightly and beta
Configure Travis to test both nightly and beta

birkenfeld/docopt.rs,zsiciarz/docopt.rs,zsiciarz/docopt.rs,zsiciarz/docopt.rs,brandonson/docopt.rs,birkenfeld/docopt.rs,brandonson/docopt.rs,birkenfeld/docopt.rs,brandonson/docopt.rs