Use of dnsruby triggers a deprecation warning under Xenial

After upgrading to Xenial, an often-run cron job that uses Dnsruby started kicking out a warning:

/usr/lib/ruby/vendor_ruby/dnsruby.rb:413: warning: constant Dnsruby::TimeoutError is deprecated

That line is:

  class ResolvTimeout < TimeoutError

Evidently, under Ruby 2.3 (the default Ruby for Xenial), TimeoutError should be Timeout::Error.

I also note that this package appears to be sourced from the old RubyForge site. The project has been moved to https://github.com/alexdalitz/dnsruby. The latest release (1.59.2) has the above problem fixed.