remove extra tilde.
remove extra tilde.

Fixes #60

gpbonillas/rust_for_rubyists,gpbonillas/rust_for_rubyists,dskecse/rust_for_rubyists,steveklabnik/rust_for_rubyists,gpbonillas/rust_for_rubyists,dskecse/rust_for_rubyists,dskecse/rust_for_rubyists,steveklabnik/rust_for_rubyists,steveklabnik/rust_for_rubyists