[ci skip] Fix documentation for deprecation method_wrappers

[ignat-z]

Seems like version with class methods doesn't work (and seems like it's correct, because of module prepending and define_method creates instance methods).

require "active_support/deprecation.rb"

module Fred
  extend self

  def aaa; end
  def bbb; end
  def ccc; end
  def ddd; end
  def eee; end
end

ActiveSupport::Deprecation.deprecate_methods(Fred, :aaa, bbb: :zzz, ccc: 'use Bar#ccc instead')
Fred.aaa
Fred.bbb
Fred.ccc

-> nothing

vs

require "active_support/deprecation.rb"

class Fred
  def aaa; end
  def bbb; end
  def ccc; end
  def ddd; end
  def eee; end
end

ActiveSupport::Deprecation.deprecate_methods(Fred, :aaa, bbb: :zzz, ccc: 'use Bar#ccc instead')
Fred.new.aaa
Fred.new.bbb
Fred.new.ccc

->

DEPRECATION WARNING: aaa is deprecated and will be removed from Rails 5.2 (called from <main> at deprications.rb:15)
DEPRECATION WARNING: bbb is deprecated and will be removed from Rails 5.2 (use zzz instead) (called from <main> at deprications.rb:16)
DEPRECATION WARNING: ccc is deprecated and will be removed from Rails 5.2 (use Bar#ccc instead) (called from <main> at deprications.rb:17)