fix set_cookie references within ref_switcher_spec.rb

spec/features/projects/ref_switcher_spec.rb

 require 'rails_helper'
 
 feature 'Ref switcher', :js do
+  include CookieHelper
+
   let(:user)      { create(:user) }
   let(:project)   { create(:project, :public, :repository) }
 
   before do
     project.team << [user, :master]
-    page.driver.set_cookie('new_repo', 'true')
+    set_cookie('new_repo', 'true')
     sign_in(user)
     visit project_tree_path(project, 'master')
   end