add hidden input

src/mechanize/form.cr

@@ -2,6 +2,7 @@ require "./form/field"
 require "./form/radio_button"
 require "./form/check_box"
 require "./form/text"
+require "./form/hidden"
 
 class MechanizeCr::Form
   getter fields     : Array(FormContent::Field)
@@ -81,6 +82,8 @@ class MechanizeCr::Form
         radiobuttons << FormContent::RadioButton.new(html_node, self)
       when "text"
         fields << FormContent::Text.new(html_node)
+      when "hidden"
+        fields << FormContent::Hidden.new(html_node)
       else
         fields << FormContent::Field.new(html_node)
       end