Build fails depending on the version of ruby zip installed

[aaime]

The output can be:

I, [2016-05-27T10:28:52.363070 #22876]  INFO -- git: Building zip file /home/aaime/devel/git-gwc/geowebcache/target/release/geowebcache-1.9.0-xsddoc.zip from directory /home/aaime/devel/git-gwc/geowebcache/target/release/geowebcache-1.9.0
release.rb:303:in `build_release': uninitialized constant Zip::File (NameError)
    from release.rb:643:in `block in <main>'
    from release.rb:610:in `each'
    from release.rb:610:in `<main>'