specify rugged version

with 0.19.0 (in rubygem-rugged-0.19.0-4.fc20.x86_64) you'll get this:

/usr/local/share/gems/gems/oxidized-0.2.2/lib/oxidized/output/git.rb:69:in `create': wrong argument type nil (expected Hash) (TypeError)
        from /usr/local/share/gems/gems/oxidized-0.2.2/lib/oxidized/output/git.rb:69:in `update_repo'
        from /usr/local/share/gems/gems/oxidized-0.2.2/lib/oxidized/output/git.rb:33:in `store'
        from /usr/local/share/gems/gems/oxidized-0.2.2/lib/oxidized/worker.rb:37:in `process'
        from /usr/local/share/gems/gems/oxidized-0.2.2/lib/oxidized/worker.rb:13:in `block in work'
        from /usr/local/share/gems/gems/oxidized-0.2.2/lib/oxidized/worker.rb:13:in `each'
        from /usr/local/share/gems/gems/oxidized-0.2.2/lib/oxidized/worker.rb:13:in `work'
        from /usr/local/share/gems/gems/oxidized-0.2.2/lib/oxidized/core.rb:36:in `run'
        from /usr/local/share/gems/gems/oxidized-0.2.2/lib/oxidized/core.rb:29:in `initialize'
        from /usr/local/share/gems/gems/oxidized-0.2.2/lib/oxidized/core.rb:11:in `new'
        from /usr/local/share/gems/gems/oxidized-0.2.2/lib/oxidized/core.rb:11:in `new'
        from /usr/local/share/gems/gems/oxidized-0.2.2/lib/oxidized/cli.rb:9:in `run'
        from /usr/local/share/gems/gems/oxidized-0.2.2/bin/oxidized:9:in `<top (required)>'
        from /usr/local/bin/oxidized:23:in `load'
        from /usr/local/bin/oxidized:23:in `<main>'