Update pretty printing.
Update pretty printing.

See https://github.com/rust-lang/rust/pull/19964.

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