Merge branch 'blackst0ne-rails5-update-active-record-locking-initializer' into 'master'

[Rails5] Update active_record_locking initializer

See merge request gitlab-org/gitlab-ce!17824

config/initializers/active_record_locking.rb

 # rubocop:disable Lint/RescueException
 
-# This patch fixes https://github.com/rails/rails/issues/26024
-# TODO: Remove it when it's no longer necessary
+# Remove this entire initializer when we are at rails 5.0.
+# This file fixes the bug (see below) which has been fixed in the upstream.
+unless Gitlab.rails5?
+  # This patch fixes https://github.com/rails/rails/issues/26024
+  # TODO: Remove it when it's no longer necessary
 
-module ActiveRecord
+  module ActiveRecord
     module Locking
       module Optimistic
         # We overwrite this method because we don't want to have default value
@@ -71,4 +74,5 @@ module ActiveRecord
         end
       end
     end
+  end
 end