uninitialized constant Wukong::Streamer (NameError)

[sergiolr100]

Hi everybody, I'm new in ruby and Wukong, I'm trying to execute this example:
https://github.com/mrflip/wukong/blob/master/examples/stats/avg_value_frequency.rb
I've installed the last version of Wukong 4.0.0 successfully.
My ruby version:
[root@sergio avf]# ruby -version
ruby 1.9.3p547 (2014-05-14 revision 45962) [x86_64-linux]
[root@sergio avf]# echo $GEM_PATH
/usr/local/rvm/gems/ruby-1.9.3-p547:/usr/local/rvm/gems/ruby-1.9.3-p547@global

but when I try to execute it:
[root@sergio avf]# ruby avg_value_frequency.rb --run=local stats.tsv avf_out.tsv
avg_value_frequency.rb:26:in <module:AverageValueFrequency>': uninitialized constant Wukong::Streamer (NameError) from avg_value_frequency.rb:22:in

'

Does anyone know what is happening? where is my mistake?