Inherit models from ApplicationRecord instead of ActiveRecord::Base.

app/models/ip_ban.rb

@@ -1,4 +1,4 @@
-class IpBan < ActiveRecord::Base
+class IpBan < ApplicationRecord
   IP_ADDR_REGEX = /\A(?:[0-9]{1,3}\.){3}[0-9]{1,3}\Z/
   belongs_to :creator, :class_name => "User"
   before_validation :initialize_creator, :on => :create