Remove dependency on Scrivito

Because `scriviton_path(Obj.root)` means `/`, we can replace to `root_url`.

Author: nalabjp

app/controllers/docs_controller.rb

@@ -7,7 +7,7 @@ def index
 
   def show
     @doc = Document.new(params[:id])
-    redirect_to scrivito_path(Obj.root) if not @doc.exists?
+    redirect_to root_url unless @doc.exists?
     @content = Kramdown::Document.new(@doc.content, input: 'GFM').to_html
     @url     = request.url
   end

spec/controllers/docs_controller_spec.rb

@@ -18,7 +18,7 @@
 
     it 'when invalid filename' do
       get :show, params: { id: '../not_found' }
-      expect(response).to redirect_to controller.scrivito_path(Obj.root)
+      expect(response).to redirect_to controller.root_url
       expect(response.status).to eq 302
     end
   end