Inherit models from ApplicationRecord instead of ActiveRecord::Base.

app/models/note_version.rb

@@ -1,4 +1,4 @@
-class NoteVersion < ActiveRecord::Base
+class NoteVersion < ApplicationRecord
   before_validation :initialize_updater
   belongs_to :updater, :class_name => "User"
   scope :for_user, lambda {|user_id| where("updater_id = ?", user_id)}