Add rubysl for rbx

Gemfile

@@ -8,6 +8,8 @@ gem 'activerecord-jdbcsqlite3-adapter', :platform => :jruby
 gem 'pry', :platform => :ruby
 gem 'pry-byebug', :platform => :ruby
 
+gem 'rubysl', :platform => :rbx
+
 # Hinting at development dependencies
 # Prevents bundler from taking a long-time to resolve
 group :development, :test do