fix uninitialized constant Fluentd::Config::DSL

bin/fluentd -c fluentd-conf.rb

    Unexpected error uninitialized constant Fluentd::Config::DSL
      /home/seo.naotoshi/gitrepos/fluentd_v11/lib/fluentd/server.rb:116:in `read_config'
      /home/seo.naotoshi/gitrepos/fluentd_v11/lib/fluentd/server.rb:76:in `reload_config'
      /home/seo.naotoshi/.rbenv/versions/2.0.0-p195/lib/ruby/gems/2.0.0/gems/serverengine-1.5.3/lib/serverengine/supervisor.rb:61:in `initialize'
      /home/seo.naotoshi/gitrepos/fluentd_v11/lib/fluentd/server.rb:68:in `initialize'
      /home/seo.naotoshi/.rbenv/versions/2.0.0-p195/lib/ruby/gems/2.0.0/gems/serverengine-1.5.3/lib/serverengine/supervisor.rb:83:in `block (2 levels) in create_server_proc'
      /home/seo.naotoshi/.rbenv/versions/2.0.0-p195/lib/ruby/gems/2.0.0/gems/serverengine-1.5.3/lib/serverengine/supervisor.rb:83:in `instance_eval'
      /home/seo.naotoshi/.rbenv/versions/2.0.0-p195/lib/ruby/gems/2.0.0/gems/serverengine-1.5.3/lib/serverengine/supervisor.rb:83:in `block in create_server_proc'
      /home/seo.naotoshi/.rbenv/versions/2.0.0-p195/lib/ruby/gems/2.0.0/gems/serverengine-1.5.3/lib/serverengine/daemon.rb:160:in `call'
      /home/seo.naotoshi/.rbenv/versions/2.0.0-p195/lib/ruby/gems/2.0.0/gems/serverengine-1.5.3/lib/serverengine/daemon.rb:160:in `create_server'
      /home/seo.naotoshi/.rbenv/versions/2.0.0-p195/lib/ruby/gems/2.0.0/gems/serverengine-1.5.3/lib/serverengine/daemon.rb:99:in `main'
      /home/seo.naotoshi/.rbenv/versions/2.0.0-p195/lib/ruby/gems/2.0.0/gems/serverengine-1.5.3/lib/serverengine/daemon.rb:90:in `run'
      /home/seo.naotoshi/gitrepos/fluentd_v11/lib/fluentd/server.rb:64:in `run'
      /home/seo.naotoshi/gitrepos/fluentd_v11/lib/fluentd/command/fluentd.rb:166:in `<top (required)>'
      /home/seo.naotoshi/.rbenv/versions/2.0.0-p195/lib/ruby/2.0.0/rubygems/core_ext/kernel_require.rb:45:in `require'
      /home/seo.naotoshi/.rbenv/versions/2.0.0-p195/lib/ruby/2.0.0/rubygems/core_ext/kernel_require.rb:45:in `require' bin/fluentd:5:in `<main>'