Add frozen_string_literal: true to email handlers

lib/gitlab/email/handler.rb

+# frozen_string_literal: true
+
 require 'gitlab/email/handler/create_merge_request_handler'
 require 'gitlab/email/handler/create_note_handler'
 require 'gitlab/email/handler/create_issue_handler'

lib/gitlab/email/handler/base_handler.rb

+# frozen_string_literal: true
+
 module Gitlab
   module Email
     module Handler

lib/gitlab/email/handler/create_issue_handler.rb

+# frozen_string_literal: true
+
 require 'gitlab/email/handler/base_handler'
 
 module Gitlab

lib/gitlab/email/handler/create_merge_request_handler.rb

+# frozen_string_literal: true
+
 require 'gitlab/email/handler/base_handler'
 require 'gitlab/email/handler/reply_processing'
 

lib/gitlab/email/handler/create_note_handler.rb

+# frozen_string_literal: true
+
 require 'gitlab/email/handler/base_handler'
 require 'gitlab/email/handler/reply_processing'
 

lib/gitlab/email/handler/reply_processing.rb

+# frozen_string_literal: true
+
 module Gitlab
   module Email
     module Handler

lib/gitlab/email/handler/unsubscribe_handler.rb

+# frozen_string_literal: true
+
 require 'gitlab/email/handler/base_handler'
 
 module Gitlab

spec/lib/gitlab/email/handler/create_issue_handler_spec.rb

+# frozen_string_literal: true
+
 require 'spec_helper'
 
 describe Gitlab::Email::Handler::CreateIssueHandler do

spec/lib/gitlab/email/handler/create_merge_request_handler_spec.rb

+# frozen_string_literal: true
+
 require 'spec_helper'
 
 describe Gitlab::Email::Handler::CreateMergeRequestHandler do

spec/lib/gitlab/email/handler/create_note_handler_spec.rb

+# frozen_string_literal: true
+
 require 'spec_helper'
 
 describe Gitlab::Email::Handler::CreateNoteHandler do

spec/lib/gitlab/email/handler/unsubscribe_handler_spec.rb

+# frozen_string_literal: true
+
 require 'spec_helper'
 
 describe Gitlab::Email::Handler::UnsubscribeHandler do

spec/lib/gitlab/email/handler_spec.rb

+# frozen_string_literal: true
+
 require 'spec_helper'
 
 describe Gitlab::Email::Handler do