Rubyzip gem no longer requires the zip class prefix

[fontno]

Just a quick fix. When I ran the rails passbook:config generator I received these errors

rails g passbook:config
/Users/Brian/forks/xl-passbook-ruby/lib/passbook/pkpass.rb:23:in `require': cannot load such file -- zip/zipfilesystem (LoadError)
    from /Users/Brian/forks/xl-passbook-ruby/lib/passbook/pkpass.rb:23:in `<top (required)>'

rails g passbook:config
/Users/Brian/forks/xl-passbook-ruby/lib/passbook/pkpass.rb:23:in `require': cannot load such file -- zipfilesystem (LoadError)
    from /Users/Brian/forks/xl-passbook-ruby/lib/passbook/pkpass.rb:23:in `<top (required)>'

It seems Rubyzip made some changes.
https://github.com/rubyzip/rubyzip#important-note

"Rubyzip interface changed!!! No need to do require "zip/zip" and Zip prefix in class names removed."

Thanks for releasing this gem. It has been a great help.