Fix SimpleForm bug when passing :name => nil as a options.

Since
f0a5d32537
if you pass :name => nil to an input it will not generate the automatic
name.

This issue was hidden because country_select has reimplemented
add_default_name_and_id on ActionView::Helpers::Tags::Base.

lib/simple_form/inputs/boolean_input.rb

@@ -49,9 +49,10 @@ module SimpleForm
       # we need the hidden field to be *outside* the label (otherwise it
       # generates invalid html - html5 only).
       def build_hidden_field_for_checkbox
-        @builder.hidden_field(attribute_name, :value => unchecked_value, :id => nil,
-                              :disabled => input_html_options[:disabled],
-                              :name => input_html_options[:name])
+        options = { value: unchecked_value, id: nil, disabled: input_html_options[:disabled] }
+        options[:name] = input_html_options[:name] if input_html_options.has_key?(:name)
+
+        @builder.hidden_field(attribute_name, options)
       end
 
       def inline_label