Fix gem

Gemfile

+source "https://rubygems.org"
+gemspec

jekyll-theme-lcsb-frozen-components.gemspec

@@ -10,7 +10,10 @@ Gem::Specification.new do |spec|
   spec.homepage      = "https://git-r3lab.uni.lu/core-services/jekyll-theme-lcsb-frozen-components"
   spec.license       = "apache2"
 
-  spec.files         = `git ls-files -z`.split("\x0").select { |f| f.match(%r!^(_plugins|LICENSE|README)!i) }
+  spec.files         = `git ls-files -z`.split("\x0").select { |f| f.match(%r!^(lib|LICENSE|README)!i) }
 
   spec.add_runtime_dependency "jekyll", "> 3.0"
+
+  spec.add_development_dependency "bundler", "~> 1.12"
+  spec.add_development_dependency "rake", "~> 10.0"
 end

lib/jekyll-theme-lcsb-frozen-components.rb

+require 'jekyll/tags/rblock'
+require 'jekyll/tags/rgridblock'
+require 'jekyll/tags/rtitle'