Auto correct rubocop offenses

Offenses:

railties/lib/rails/autoloaders.rb:1:1: C: [Corrected] Style/FrozenStringLiteralComment: Missing magic comment # frozen_string_literal: true.
module Rails
^
actionmailer/test/base_test.rb:917:1: C: [Corrected] Layout/EmptyLinesAroundBlockBody: Extra empty line detected at block body beginning.
actionmailer/test/base_test.rb:917:1: C: [Corrected] Layout/TrailingWhitespace: Trailing whitespace detected.
actionmailer/test/base_test.rb:917:5: C: [Corrected] Style/RedundantBegin: Redundant begin block detected.
    begin
    ^^^^^
actionmailer/test/base_test.rb:918:3: C: [Corrected] Layout/IndentationWidth: Use 2 (not 4) spaces for indentation.
      events = []
  ^^^^
actionmailer/test/base_test.rb:930:1: C: [Corrected] Layout/EmptyLinesAroundBlockBody: Extra empty line detected at block body end.
actionmailer/test/base_test.rb:930:1: C: [Corrected] Layout/TrailingWhitespace: Trailing whitespace detected.

actionmailer/test/base_test.rb

@@ -914,20 +914,18 @@ def a_callback
   end
 
   test "notification for deliver" do
-    begin
-      events = []
-      ActiveSupport::Notifications.subscribe("deliver.action_mailer") do |*args|
-        events << ActiveSupport::Notifications::Event.new(*args)
-      end
+    events = []
+    ActiveSupport::Notifications.subscribe("deliver.action_mailer") do |*args|
+      events << ActiveSupport::Notifications::Event.new(*args)
+    end
 
-      BaseMailer.welcome(body: "Hello there").deliver_now
+    BaseMailer.welcome(body: "Hello there").deliver_now
 
-      assert_equal 1, events.length
-      assert_equal "deliver.action_mailer", events[0].name
-      assert_not_nil events[0].payload[:message_id]
-    ensure
-      ActiveSupport::Notifications.unsubscribe "deliver.action_mailer"
-    end
+    assert_equal 1, events.length
+    assert_equal "deliver.action_mailer", events[0].name
+    assert_not_nil events[0].payload[:message_id]
+  ensure
+    ActiveSupport::Notifications.unsubscribe "deliver.action_mailer"
   end
 
   private

railties/lib/rails/autoloaders.rb

@@ -1,3 +1,5 @@
+# frozen_string_literal: true
+
 module Rails
   module Autoloaders # :nodoc:
     class << self