Fix 'defaults' option for root route

The merging of the 'defaults' option was moved up the stack in e852daa6
This allows us to see where these options originate from the standard
HttpHelpers (get, post, patch, put, delete)

Unfortunately this move didn't incorporate the 'root' method, which has
always allowed the same 'defaults' option before.

actionpack/lib/action_dispatch/routing/mapper.rb

@@ -1923,7 +1923,14 @@ def path_scope(path)
 
         def match_root_route(options)
           name = has_named_route?(:root) ? nil : :root
-          match '/', { :as => name, :via => :get }.merge!(options)
+          defaults_option = options.delete(:defaults)
+          args = ['/', { :as => name, :via => :get }.merge!(options)]
+
+          if defaults_option
+            defaults(defaults_option) { match(*args) }
+          else
+            match(*args)
+          end
         end
       end
 

actionpack/test/dispatch/routing_test.rb

@@ -1759,6 +1759,24 @@ def test_default_integer_params
     assert_equal 1, @request.params[:page]
   end
 
+  def test_keyed_default_string_params_with_root
+    draw do
+      root :to => 'pages#show', :defaults => { :id => 'home' }
+    end
+
+    get '/'
+    assert_equal 'home', @request.params[:id]
+  end
+
+  def test_default_string_params_with_root
+    draw do
+      root :to => 'pages#show', :id => 'home'
+    end
+
+    get '/'
+    assert_equal 'home', @request.params[:id]
+  end
+
   def test_resource_constraints
     draw do
       resources :products, :constraints => { :id => /\d{4}/ } do