Use dup instead of new for Head Route

lib/grape/endpoint.rb

@@ -151,7 +151,8 @@ def mount_in(router)
       routes.each do |route|
         router.append(route.apply(self))
         if !namespace_inheritable(:do_not_route_head) && route.request_method == Rack::GET
-          Grape::Router::Route.new(Rack::HEAD, route.origin, route.attributes).then do |head_route|
+          route.dup.then do |head_route|
+            head_route.convert_to_head_request!
             router.append(head_route.apply(self))
           end
         end

lib/grape/router/route.rb

@@ -15,6 +15,10 @@ def initialize(method, pattern, options)
         super(options)
       end
 
+      def convert_to_head_request!
+        @request_method = Rack::HEAD
+      end
+
       def exec(env)
         @app.call(env)
       end