Fix docopt_macros for latest nightly.
Fix docopt_macros for latest nightly.

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