Add ruby-debug19 for mri 1.9

Gemfile

@@ -24,6 +24,10 @@ platforms :mri_18 do
   gem "ruby-debug", ">= 0.10.3"
 end
 
+platforms :mri_19 do
+  gem "ruby-debug19"
+end
+
 platforms :ruby do
   gem 'json'
   gem 'yajl-ruby'