Update for recent changes in libsyntax
Update for recent changes in libsyntax

See https://github.com/rust-lang/rust/pull/27234

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