Require-Gem in Ruby Filter fails

Hi there
I have set-up my ELK-Stack on my Macbook and its working good. I am now trying to improve the pre-processing of my logs in Logstash; I try to count Emoji's with the ruby-gem "emoji_data". If i create a ruby-filter with either a init => "require 'emoji_data'" or having the same line in the code-block itself, it always says "could not find gem 'emoji_data' java. Ruby is installed with rbenv and i am currently using both, ruby 2.2.3 and jruby, the gem from above is installed in both environments and i can use it in irb or standalone scripts.

any ideas? I already added it to the Gemfile, but then - as soon i execute bundler - it tells me the same thing while bundler runs... i'm stuck :confused:

Thanks for your help