Add user login with facebook spec
user
```ruby
require 'rails_helper'

module Pwb

  RSpec.feature "user logs in" do
    # http://www.jessespevack.com/blog/2016/10/16/how-to-test-drive-omniauth-google-oauth2-for-your-rails-app
    scenario "using facebook oauth2" do
      stub_omniauth
      # visit root_path
      visit('/admin')
      # puts current_url

      expect(page).to have_link("Sign in with Facebook")
      click_link "Sign in with Facebook"
      expect(page).to have_content("You need to be an admin to access this")
      # expect(page).to have_link("Logout")
    end

    def stub_omniauth
      # first, set OmniAuth to run in test mode
      OmniAuth.config.test_mode = true
      # then, provide a set of fake oauth data that
      # omniauth will use when a user tries to authenticate:
      OmniAuth.config.mock_auth[:facebook] = OmniAuth::AuthHash.new({
                                                                    provider: "facebook",
                                                                    uid: "12345678910",
                                                                    info: {
                                                                      email: "dummy@dummy.com",
                                                                      first_name: "Ed",
                                                                      last_name: "Tee"
                                                                    },
                                                                    credentials: {
                                                                      token: "abcdefg12345",
                                                                      refresh_token: "12345abcdefg",
                                                                      expires_at: DateTime.now
                                                                    }
      })
    end
  end

end
```
assistant