capistrano error

cap -T
/usr/lib/ruby/gems/1.8/gems/sshkit-1.1.0/lib/sshkit.rb:32: undefined method `require_relative' for main:Object (NoMethodError)
    from /usr/local/lib/site_ruby/1.8/rubygems/core_ext/kernel_require.rb:55:in `gem_original_require'
    from /usr/local/lib/site_ruby/1.8/rubygems/core_ext/kernel_require.rb:55:in `require'
    from /usr/lib/ruby/gems/1.8/gems/capistrano-3.0.0/lib/capistrano/all.rb:2
    from /usr/local/lib/site_ruby/1.8/rubygems/core_ext/kernel_require.rb:55:in `gem_original_require'
    from /usr/local/lib/site_ruby/1.8/rubygems/core_ext/kernel_require.rb:55:in `require'
    from /usr/lib/ruby/gems/1.8/gems/capistrano-3.0.0/bin/cap:2
    from /usr/local/bin/cap:19:in `load'
    from /usr/local/bin/cap:19