include ruby-debug in list of gems needed to run features / specs

geminstaller.yml

@@ -6,4 +6,4 @@ gems:
 - { name: 'rspec',                   version: '>= 1.2.9' }
 - { name: 'rspec-rails',             version: '>= 1.2.9' }
 - { name: 'rails',                   version: '>= 2.3' }
-
+- { name: 'ruby-debug',              version: '>= 0.10.3' }