dashirizing non value directives key

lib/lotus/action/cache_control/directives.rb

@@ -42,7 +42,7 @@ def initialize(name)
         end
 
         def to_str
-          @name
+          @name.to_s.tr('_', '-')
         end
 
         def valid?

test/unit/cache_control/directives_test.rb

@@ -127,3 +127,12 @@
     end
   end
 end
+
+describe 'NonValueDirective' do
+  describe '#to_str' do
+    it 'returns as http cache format' do
+      subject = Lotus::Action::CacheControl::NonValueDirective.new(:no_cache)
+      subject.to_str.must_equal('no-cache')
+    end
+  end
+end