rename factory_girl_(rails) to factory_bot_(rails)

spec/mailers/user_mailer_spec.rb

@@ -1,7 +1,7 @@
 require 'rails_helper'
 
 describe UserMailer do
-  let(:user) { InternalUser.create(FactoryGirl.attributes_for(:teacher)) }
+  let(:user) { InternalUser.create(FactoryBot.attributes_for(:teacher)) }
 
   describe '#activation_needed_email' do
     let(:mail) { described_class.activation_needed_email(user) }