Fix deprecation warning (#48)

While working on a new feature for modis (#49) I noticed that calling
`deprecate` without passing in a deprecator instance is deprecated.
Thought I would address this apart from the larger feature PR.

lib/modis.rb

@@ -7,6 +7,7 @@
 require 'msgpack'
 
 require 'modis/version'
+require 'modis/deprecator'
 require 'modis/configuration'
 require 'modis/attribute'
 require 'modis/errors'

lib/modis/deprecator.rb

@@ -0,0 +1,7 @@
+# frozen_string_literal: true
+
+module Modis
+  def self.deprecator
+    @deprecator ||= ActiveSupport::Deprecation.new('5.0', 'modis')
+  end
+end

lib/modis/persistence.rb

@@ -166,15 +166,15 @@ def update(attrs)
     end
 
     alias update_attributes update
-    deprecate update_attributes: 'please, use update instead'
+    deprecate update_attributes: 'please, use update instead', deprecator: Modis.deprecator
 
     def update!(attrs)
       assign_attributes(attrs)
       save!
     end
 
     alias update_attributes! update!
-    deprecate update_attributes!: 'please, use update! instead'
+    deprecate update_attributes!: 'please, use update! instead', deprecator: Modis.deprecator
 
     private