Add missing require to reactive-ruby

Author: zetachang

lib/reactive-ruby.rb

@@ -22,6 +22,7 @@
   require 'react/observable'
   require 'react/component'
   require 'react/component/dsl_instance_methods'
+  require 'react/component/should_component_update'
   require 'react/component/tags'
   require 'react/component/base'
   require 'react/element'