Add HPKP headers

Author: naiyt

lib/secure_headers/railtie.rb

@@ -7,7 +7,7 @@ class Railtie < Rails::Engine
                              'X-Permitted-Cross-Domain-Policies', 'X-Download-Options',
                              'X-Content-Type-Options', 'Strict-Transport-Security',
                              'Content-Security-Policy', 'Content-Security-Policy-Report-Only',
-                             'X-Permitted-Cross-Domain-Policies']
+                             'X-Permitted-Cross-Domain-Policies','Public-Key-Pins','Public-Key-Pins-Report-Only']
 
       initializer "secure_headers.action_controller" do
         ActiveSupport.on_load(:action_controller) do