https: Point to the logo using https instead of http

This is needed to not have paypal's checkout patch fetch from
a http source during checkout.

app/controllers/spree/checkout_controller_decorator.rb

@@ -201,7 +201,7 @@ module Spree
     private
 
     def asset_url(_path)
-      URI::HTTP.build(:path => ActionController::Base.helpers.asset_path(_path), :host => Spree::Config[:site_url].strip).to_s
+      URI::HTTPS.build(:path => ActionController::Base.helpers.asset_path(_path), :host => Spree::Config[:site_url].strip).to_s
     end
 
     def record_log(payment, response)