w3c_validators 1.3 don't support Ruby 1.9

Gemfile

@@ -40,7 +40,7 @@ gem 'mime-types', '< 3', require: false
 group :doc do
   gem 'sdoc', '>= 1.0.0.rc1', '< 1.1'
   gem 'redcarpet', '~> 3.1.2', platforms: :ruby
-  gem 'w3c_validators'
+  gem 'w3c_validators', RUBY_VERSION < '2.0' ? '1.2' : nil
   gem 'kindlerb', '0.1.1'
   gem 'mustache', '~> 0.99.8'
 end

Gemfile.lock

@@ -126,7 +126,7 @@ GEM
       rails-dom-testing (>= 1, < 3)
       railties (>= 4.2.0)
       thor (>= 0.14, < 2.0)
-    json (2.0.2)
+    json (2.1.0)
     kindlerb (0.1.1)
       mustache
       nokogiri
@@ -295,4 +295,4 @@ DEPENDENCIES
   w3c_validators
 
 BUNDLED WITH
-   1.14.4
+   1.15.1