Update yard ~> 0.9.12 due to vulnerability.

Author: gkellogg

rdf-spec.gemspec

@@ -32,6 +32,6 @@ Gem::Specification.new do |gem|
   gem.add_runtime_dependency     'rspec',           '~> 3.7'
   gem.add_runtime_dependency     'rspec-its',       '~> 1.2'
   gem.add_runtime_dependency     'webmock',         '~> 3.0'
-  gem.add_development_dependency 'yard' ,           '~> 0.8'
+  gem.add_development_dependency 'yard' ,           '~> 0.9.12'
   gem.post_install_message       = nil
 end