Gemfile in wisper-1.2.1 vs Gemfile in wisper-1.3.0

@@ -1,8 +1,10 @@
 source 'https://rubygems.org'
 
 gemspec
 
+gem 'rubysl', '~> 2.0', :platforms => :rbx
+
 group :metrics do
   gem 'simplecov'
   gem 'flay'
 end